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Generac GT-990 Engine

The Generac GT-990 is a 0.99 L 2-cylinder air-cooled engine rated at 3600 rpm, producing up to 18.6 kW. It powers generator sets from Generac and Power Systems, including the 8.1 GN, Model 004666 and Model 005011. It holds 1.5 L (0.4 gal) of oil.

Also known as: Generac GT-990, GT-990

Part of the Generac GT990 engine family — 3 variants share parts & fitment.

0.992 L

Displacement

Cylinders

3600 rpm

Rated speed

18 kW

Gross power

On this pageSpecs Generator sets Maintenance FAQ Service intervals Torque & specs Fluids Fault codes Procedures Wiring

Engine specifications

Oil capacity	1.5 L
Displacement	0.992 L
Cylinders	2
Aspiration	Air-cooled
Rated speed	3600 rpm
Gross power	18 kW

Generator sets powered by this engine

Shared across brands: Generac, Power Systems

Generac 8.1 GNGenerac Model 004666Generac Model 005011Power Systems GT-990

How to read your Generac engine serial & model number →

Troubleshooting

Fault codes

Code	Meaning	Cause	Remedy
F1	Blown F1 or F2 fuse		Check fuse F1 & F2 (Test 30); check N1 & N2 wiring (Test 34); check transformer TX (Test 35); repair or replace; replace
F2	Blown F1 or F2 fuse		Check fuse F1 & F2 (Test 30); check N1 & N2 wiring (Test 34); check transformer TX (Test 35); repair or replace; replace
F1	15 Amp fuse (F1) blown	Fuse blows immediately when replaced; fuse blows when placed in "AUTO" or "MANUAL"	Check battery voltage circuit (Test 75); check cranking and running circuits (Test 76)

Symptoms & remedies

Symptom	Cause	Remedy
Generator produces zero voltage or residual voltage		Perform fixed excitation / rotor amp draw test (Test 4); test stator (Test 7); test rotor assembly (Test 10); perform stator insulation resistance test (Section 1.4); perform rotor insulation resistance test (Section 1.4); check VOM fuses; repair or replace fuses; reset to "ON" or replace if bad; check brushes & slip rings (Test 9); test wire continuity (Test 5); field boost (Test 6); check rotor circuit (Test 8); repair or replace
Generator produces low voltage at no-load		Check AC output frequency (Test 11); adjust engine governor (Test 12); check stepper motor control (Test 12A); check AC output voltage (Test 2); adjust voltage regulator (Test 13); if frequency OK but voltage still low, go to Problem 1 flow chart starting at Test 4 - F/E; replace defective voltage regulator
Generator produces high voltage at no-load		Check AC output frequency (Test 11); adjust engine governor (Test 12); check stepper motor control (Test 12A); check AC output voltage (Test 2); adjust voltage regulator (Test 13); replace defective voltage regulator
Voltage and frequency drop excessively when loads are applied	Overload condition; idle control transformer defective; LC1 & LC2 wiring defective; idle control transformer primary wiring defective; engine condition (dirty air cleaner, loss of compression, faulty fuel settings, incorrect ignition timing); stepper motor control; stator AC power windings	Check voltage and frequency under load (Test 14); check for overload condition (Test 15) — reduce loads to unit's rated capacity; look for a shorted condition in a connected load or in one of the load circuits; check idle control transformer (Test 79) — repair or replace the idle control transformer; check LC1 & LC2 wiring (Test 80) — repair or replace defective wiring; check idle control transformer primary wiring (Test 81) — repair or replace defective wiring; check and adjust engine governor (Test 12); go to Problem 11 - Engine Starts Hard and Runs Rough/Lacks Power, Section 4.3; check stepper motor control (Test 12A); check stator AC power windings (Test 7); if reconfigured to LP gas, verify that proper procedure was followed (refer to Section 1.3)
In automatic mode, no transfer to standby	No AC output to transfer switch from generator; C2 coil voltage good but no transfer; C2 coil voltage bad / limit switch XB1 voltage good; C2 coil voltage bad / limit switch XB1 voltage bad	Check voltage at terminal lugs E1 & E2 (Test 21); check voltage at standby closing coil C2 and limit switch XB1 (Test 22); check manual transfer switch operation (Test 24); check #23 and #194 wiring connections (Test 26); test transfer relay (Test 23); continuity test of wiring (C2) (Test 33); test limit switch XB1 (Test 25); replace limit switch; replace standby coil C2; repair wire #B; find cause of no AC output to transfer switch from generator; repair or replace
In automatic mode, generator starts when loss of utility occurs, generator shuts down when utility returns but there is no retransfer to utility power	C1 coil voltage good but no transfer; C1 coil voltage bad / limit switch XA1 voltage good; C1 coil voltage bad / limit switch XA1 voltage bad	Check voltage at utility closing coil C1 and limit switch XA1 (Test 29); check manual transfer switch operation (Test 24); check #23 and #194 wiring connections (Test 26); test transfer relay (Test 23); continuity test of wiring (C1) (Test 32); test limit switch XA1 (Test 31); replace limit switch; replace utility coil C1; repair wire #A; repair or replace
Engine will not crank when utility power source fails	AUTO-OFF-MANUAL switch is OFF; AUTO-OFF-MANUAL switch bad; wire 15/15A/15B/239/0 voltage bad; printed circuit board defective	Verify utility source is "OFF"; system ready light should be flashing; check position of AUTO-OFF-MANUAL switch (Test 41) — set to "AUTO" - retest; turn "OFF" - retest; try a manual start (Test 42) — go to Problem 9; test AUTO-OFF-MANUAL switch (Test 43) — replace; check wire 15/15A/15B/239/0 voltage (Test 44) — replace printed circuit board
Engine will not crank when AUTO-OFF-MANUAL switch is set to "MANUAL"	Battery low; 15 amp fuse bad; AUTO-OFF-MANUAL switch bad; wire 15/15A/15B/239/0 voltage bad; starter motor bad; wire 56 voltage bad; starter contactor relay (V-twin only) bad; starter contactor bad	Check battery - low battery LED should be off (Test 46) — recharge / replace; check 15 amp fuse (Test 45) — replace; test AUTO-OFF-MANUAL switch (Test 43) — replace; check wire 15/15A/15B/239/0 voltage (Test 44) — replace printed circuit board; test starter motor (Test 50) — repair / replace; check wire 56 voltage (Test 47) — replace; check starter contactor relay (V-twin only) (Test 48) — replace; check starter contactor (Test 49) — replace
Engine cranks but won't start	Fuel supply and pressure bad; fuel regulator bad; no ignition spark; choke solenoid bad; ignition magnetos out of adjustment; shutdown wire shorted; valves out of adjustment; spark plugs bad; engine compression bad; fuel solenoid bad; circuit board wire 14 output bad; air filter dirty; stepper motor control bad; flywheel key sheared	Check fuel supply and pressure (Test 51) — find and correct cause of no fuel or low pressure; check fuel regulator (Test 63) — repair or replace; check for ignition spark (Test 55) — repair or replace; check choke solenoid (Test 54) — replace choke solenoid; check and adjust ignition magnetos (Test 59) — adjust or replace; check shutdown wire (Test 58) — repair or replace shorted wire 18 or circuit board; check and adjust valves (Test 62) — readjust; check spark plugs (Test 56) — clean, regap or replace; check engine compression (Test 57) — refer to engine service manual; check fuel solenoid (Test 53) — replace fuel solenoid; check circuit board wire 14 output (Test 52) — replace circuit board; check air filter - replace as needed; check stepper motor control (Test 12A); check flywheel key (Test 59)
Engine starts hard and runs rough / lacks power	Fuel regulator bad; fuel supply and pressure bad; no ignition spark; ignition magnetos out of adjustment; valves out of adjustment; spark plugs bad; engine compression bad; choke solenoid bad; air filter dirty; stepper motor control bad; engine governor out of adjustment; flywheel key sheared; improper LP gas reconfiguration procedure	Check fuel regulator (Test 63) — repair or replace; check fuel supply and pressure (Test 51) — find and correct cause of no fuel or low pressure; check for ignition spark (Test 55) — repair or replace; check and adjust ignition magnetos (Test 59) — adjust or replace; check and adjust valves (Test 62) — readjust; check spark plugs (Test 56) — clean, regap or replace; check engine compression (Test 57) — refer to engine service manual; check choke solenoid (Test 54) — replace choke solenoid; check air filter - replace as needed; check stepper motor control (Test 12A); check and adjust engine governor (Test 12); check flywheel key (Test 59); if reconfigured to LP gas, verify that proper procedure was followed (refer to Section 1.3)
Engine starts and runs, then shuts down	Low oil; over temperature; overspeed; no fuel or low pressure; no ignition spark; ignition magnetos out of adjustment; shutdown wire shorted; engine governor out of adjustment; stepper motor control bad; wire 18 continuity bad; AC output frequency bad; installation airflow improper or defective switch	Check fault lights; check oil pressure switch and wire 86 (Test 60) — repair or replace; check high oil temperature switch (Test 61) — repair or replace; check fuel supply and pressure (Test 51) — find and correct cause of no fuel or low pressure; check for ignition spark (Test 55) — repair or replace; check and adjust ignition magnetos (Test 59) — adjust or replace; check shutdown wire (Test 58) — repair or replace shorted wire 18 or circuit board; check and adjust engine governor (Test 12) — readjust; check stepper motor control (Test 12A); check wire 18 continuity (Test 70) — replace PCB; check AC output frequency (Test 11) — refer to engine service manual; check installation for proper airflow or replace defective switch; repair linkage if binding, check throttle operation
No battery charge	Transformer (TX) voltage output bad; AC voltage at battery charger bad; battery charge relay bad; battery charger wiring bad; battery charge winding harness bad; stator bad; battery charge regulator bad	Check battery charge output (Test 64); test transformer (TX) voltage output (Test 65) — replace; check AC voltage at battery charger (Test 66) — replace; test battery charge relay (Test 67) — replace battery charge regulator; verify battery charge relay wired correctly (see Test 66 - Step 5); check battery charger wiring (Test 69) — rewire; test battery charge winding harness (Test 68) — replace; test stator (Test 7) — repair or replace wiring; insulation resistance test, Section 1.4
Unit starts and transfer occurs when utility power is available	Transformer (TX) voltage output bad; utility sensing voltage at circuit board bad; N1 & N2 voltage bad; utility 1 & utility 2 terminals bad; voltage at terminal lugs N1 & N2 bad; fuse F1 & F2 bad	Test transformer (TX) voltage output (Test 65) — replace; check utility sensing voltage at circuit board (Test 72) — replace circuit board; check N1 & N2 voltage (Test 71) — correct utility source voltage; check utility 1 & utility 2 terminals (Test 28) — replace; check voltage at terminal lugs N1 & N2 (Test 27) — go to Problem 7, Section 3.3; check fuse F1 & F2 (Test 30) — repair or replace wiring; repair or replace wire N1A/N2A between N1/N2 lugs and fuse holder; repair N1/N2 open wiring between transfer switch and generator; replace or correct wiring
Generator starts immediately in auto - no transfer to standby, utility voltage is present	AUTO-OFF-MANUAL switch bad	Test AUTO-OFF-MANUAL switch (Test 43) — replace
Generator will not exercise		Test exercise function (Test 77)
No low speed exercise		Check DIP switch settings (Test 78)
Generator will not start when Set Exercise (SW2) switch is held		Go to Test 73; retest after performing Test 73; if the generator still will not start, replace the circuit board
Exercise fails to operate after depressing the Set Exercise switch		Wait one week and watch for exercise operation; if exercise fails to operate, replace the circuit board
Generator still will not low speed exercise (16 and 18 kW units)	Printed circuit board not set for low speed operation	Verify Dip Switch one is in the OFF position; if the dip switch is reset, remove Fuse (F1) first, set dip switch, then replace F1; if the dip switch was set correctly, remove fuse F1 for 15 seconds then replace; if the generator still will not low speed exercise, replace the printed circuit board
Idle Control Transformer resistance not approximately 50 ohms	Defective Idle Control Transformer	Repair or replace the Idle Control Transformer; refer back to Flow Chart
No CONTINUITY on Wire LC1 (red) or Wire LC2 (black) between In-Line Connector (IC) and J1 Connector	Defective wiring	Repair or replace defective wiring; refer back to Flow Chart
Idle Control Transformer primary wiring incorrect	Wires 11 and 44 do not cross through the Idle Control Transformer (ICT) from opposite sides	Correct the wiring of Wires 11 and 44 through the Idle Control Transformer (ICT) per Wiring Diagram 0F7822; if wiring checks good, replace the printed circuit board

Fault codes and symptom→remedy steps extracted from this engine’s service/owner documentation; verify against the official manual before servicing.

Common problems

Unit will not start in AUTO with utility loss NOT ACTIVATED
Fix: Refer to activation section in owners manual.
Engine cranks but won't start
Cause: Fuel supply and pressure faulty
Fix: Test 66 - Check fuel supply and pressure; find and correct cause of no fuel or low pressure
Generator produces zero voltage or residual voltage (12-20 kW)
Cause: Main circuit breaker open or failed
Fix: Reset to "ON" or replace if bad
Engine starts hard and runs rough / lacks power / backfires
Cause: Fuel supply and pressure faulty
Fix: Test 66 - Check fuel supply and pressure; find and correct cause of no fuel or low pressure
Engine will not crank when AUTO-OFF-MANUAL switch is set to "MANUAL"
Cause: Battery faulty
Fix: Test 61 - Check battery; replace
The engine cranks but will not start
Cause: Out of fuel
Fix: Replenish fuel.
The engine will not crank
Cause: Fuse blown
Fix: Replace fuse.
Voltage and frequency drop excessively when loads are applied
Cause: Overload condition
Fix: Reduce loads to unit's rated capacity; look for a shorted condition in a connected load or in one of the load circuits
Yellow LED illuminated in any state LOW BATTERY
Fix: Clear alarm. Check the battery using the control panel under the MAIN menu using the BATTERY MENU option. If it states battery is GOOD contact servicing dealer. If it states CHECK BATTERY replace the battery.
Unit consumes large amounts of oil
Cause: Break-in procedure not followed (see Section 2.1)
Fix: Contact the nearest Authorized Dealer for assistance
There is no transfer to standby after utility source failure
Cause: Defective transfer switch coil
Fix: Contact the nearest Authorized Dealer for assistance
The engine starts hard and runs rough
Cause: Air cleaner plugged or damaged
Fix: Check, replace air cleaner.
Shutdown alarm/fault occurred
Cause: AC output frequency faulty (single cylinder units)
Fix: Test 14 - Check AC output frequency; refer to engine service manual
In automatic mode, generator starts when loss of utility occurs, generator shuts down when utility returns but there is no retransfer to utility power OR generator transfers to standby during exercise or in manual mode
Cause: Manual transfer switch operation faulty
Fix: Test 27 - Check manual transfer switch operation; repair or replace as needed
Generator produces low voltage at no-load
Cause: AC output frequency low (single cylinder units)
Fix: Test 15 - Adjust engine governor

Compiled from service & troubleshooting documentation across every generator set that uses the Generac GT-990.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter			0C8127		Amazon eBay $15.99 NAPA $24.03 FridayParts $21.87
Fuel filter	Generac OE		924-0371	50 hr	Amazon eBay
Oil filter			70185		Amazon eBay $18.99 NAPA $9.09 KuduParts $11.00
Battery	12V, 75Ah		924-0380	600 hr	Amazon eBay
Belt			924-0365	1000 hr	Amazon eBay
Coolant	Generac OE		924-0370	1000 hr	Amazon eBay
Oil	Change the engine oil.	4.31 L	—	150 hr
Spark plug			—	1000 hr

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Service intervals

Item	Action	Hours	Months	Notes
Engine oil level	Check	8 hr		Check before each use / at least every 8 hours
Oil and oil filter	Change	8 hr		First service — First 8 hours of operation
Oil level	Check	24 hr	1 mo	Monthly or every 24 hours of continuous operation
Aceite del motor	Change	25 hr		First service — Después del período de asentamiento de 25 horas, se recomienda utilizar el aceite 5W-20 propiedad de Generac para uso continuo.
Oil and filter	Change	25 hr		First service — After first 25 hours of operation
Engine governor oil level	Check	50 hr		Check prior to initial use and every 50 operating hours thereafter.
Engine oil and filter	Replace	100 hr	12 mo	First service — After first 25 hours; then every 100 hours or 1 year. Cold weather (<4.4°C) or continuous hot (>29.4°C): every 100 hours or 1 year
Engine oil and oil filter	Change	400 hr	48 mo	First service — Thereafter; every season
Aceite de motor y filtro de aceite	Change	200 hr	24 mo	First service — Programa de mantenimiento A
Batería (condición, nivel de electrolito y estado de carga)	Check	200 hr	24 mo	Programa de mantenimiento A
Battery condition	Check	200 hr	24 mo	Schedule A.
Battery condition and charge	Check	200 hr	24 mo	Schedule A maintenance
Change Air Filter	Change	200 hr		200 hours or 2 years
Change Oil & Filter	Change	200 hr		200 hours or 2 years; 20kW: 100 hours or 2 years
Engine oil	Change	200 hr	24 mo	First service — Up to a 2 year/200 hour oil change interval.
Huile à moteur et filtre à huile	Change	200 hr	24 mo	First service — Calendrier A: tous les deux ans ou toutes les 200 heures. Changer l'huile et le filtre après les 25 premières heures. En conditions froides (moins de 4,4 °C/40 °F) ou fonctionnant en continu à plus de 29,4 °C/85 °F, changer annuellement ou toutes les 100 heures.
Inspect Air Filter	Inspect	200 hr		200 hours or 2 years
Inspect Spark Plugs	Inspect	200 hr		200 hours or 2 years
Oil	Change	200 hr	24 mo	First service — Every 2 years or 200 hours; change after first 8 hours then every 200 hrs/2 yrs thereafter, more often under heavy load, dust, or high temp
Oil filter	Change	200 hr	24 mo	First service — Every 2 years or 200 hours
Oil filter	Replace	200 hr	24 mo	200 hours or 2 years, whichever occurs first
Óleo lubrificante e filtro de óleo	Change	200 hr	24 mo	First service — Trocar após as primeiras 25 horas; Programação A (2 anos ou 200 h); em clima frio (<4,4 °C) ou quente contínuo (>29,4 °C) anualmente ou 100 h
Aceite del motor y filtro de aceite	Replace	400 hr	48 mo	First service — Programa B: cada cuatro años o 400 horas.
Air cleaner	Clean	400 hr		Clean or replace as necessary; R = Replace as Necessary; 400 hours
Air filter	Replace	400 hr	48 mo	Schedule B maintenance
Battery condition, electrolyte level, and state of charge	Inspect	400 hr	48 mo	Schedule B
Bougies d'allumage	Clean	400 hr	48 mo	Nettoyer les bougies, vérifier l'écartement ou les remplacer. Calendrier A et Calendrier B.
Bujía(s)	Replace	400 hr	48 mo	Programa B: cada cuatro años o 400 horas.
Bujías	Replace	400 hr	48 mo	Programa B; limpiar, comprobar separación y sustituir
Change spark Plugs	Change	400 hr		400 hours or 10 years
Engine air filter	Replace	400 hr	48 mo	Schedule B; emissions-critical maintenance
Engine oil and oil filter	Replace	400 hr	48 mo	First service — Schedule B
Filtre à air du moteur	Replace	400 hr	48 mo	Calendrier B: tous les quatre ans ou toutes les 400 heures.
Filtro de aire del motor	Replace	400 hr	48 mo	Programa de mantenimiento B
Filtro de ar do motor	Replace	400 hr	48 mo	Programação B (4 anos ou 400 h)
Folga da válvula	Adjust	400 hr	48 mo	First service — Inspecionar/ajustar após as primeiras 25 h e depois a cada 400 h; Programação B; exclui 14/18 kW com motor 816 cc
Jeu des soupapes	Adjust	400 hr		First service — Vérifier et régler après les 25 premières heures de fonctionnement, puis toutes les 400 heures.
Luz de válvulas	Adjust	400 hr	48 mo	First service — Programa B; inspeccionar/ajustar cada 400 horas
Sediment trap	Clean	400 hr	48 mo	Schedule B maintenance
Separación de la válvula	Adjust	400 hr	48 mo	First service — Programa B. Inspeccione y ajuste después de las primeras 25 horas y luego cada 400 horas. No necesario en unidades 14/18 kW con motor 816 cc.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Valve clearance	0.002 - 0.004 inch (0.05 - 0.1 mm)	inch (mm)	engine cool
Gap	Armature Air Gap	0.008-0.012	inch
Gap	Breaker Point Gap	0.018-0.022	inch
Gap	Folga da vela de ignição	0,020	pol
Gap	Folga da vela de ignição	0,040	pol
Gap	Folga da vela de ignição	0,508	mm
Gap	Folga da vela de ignição	1,02	mm
Gap	Ignition magneto (armature) air gap	0.008-0.012	inch (0.20-0.30 mm)
Gap	Ignition magneto (armature) air gap	0.008-0.012 inch (0.20-0.30mm)	inch	V-twin engines; not adjustable on single cylinder engines
Gap	Ignition magneto air gap	0.008-0.012	inch
Gap	Ignition magneto air gap	0.008-0.012 inch (0.20-0.30 mm)	gap	V-twin engines; fixed non-adjustable on single cylinder
Gap	Ignition magneto air gap (V-twin)	0.008-0.012 inch (0.20-0.30 mm)	inch / mm
Gap	Ignition magneto gap to flywheel (replacement)	0.010 inch	inch
Gap	Magneto gap between flywheel	0.010	inch
Gap	Separación de electrodos de bujía (11 kW)	0.030	in (0.76 mm)
Gap	Separación de electrodos de bujía (16/20/22 kW)	0.040	in (1.02 mm)
Gap	Separación de electrodos de bujía (9 kW)	0.020	in (0.508 mm)
Gap	Separación de las bujías	0.508	mm (0.020 pulg.)
Gap	Separación de las bujías	1.02	mm (0.040 pulg.)
Gap	Spark Plug Gap	0.030	in (0.76 mm)	11 kW (GTH-530)
Gap	Spark Plug Gap	0.031-0.035	inch
Gap	Spark plug gap	0.020	in (0.508 mm)
Gap	Spark plug gap	0.020 in (0.508 mm)	in (mm)
Gap	Spark plug gap	0.040	in (1.02 mm)
Gap	Spark plug gap	0.040 in (1.02 mm)	in (mm)
Gap	Spark plug gap	0.50	mm (0.020 inch)
Gap	Spark plug gap	0.508	mm
Gap	Spark plug gap	0.76	mm (0.030 inch)
Gap	Spark plug gap	0.76 mm (0.030 inch)	gap	410 cc and 530 cc engines
Gap	Spark plug gap	1.02	mm (0.040 inch)
Gap	Spark plug gap	1.02 mm (0.040 inch)	gap	990 cc and 999 cc engines
Gap	Spark plug gap (10 kW)	0.020	in (0.508 mm)
Gap	Spark plug gap (11 kW)	0.030	in (0.76 mm)
Gap	Spark plug gap (12/14/16/17/20 kW)	1.02	mm
Gap	Spark plug gap (12/15 kW)	0.508	mm (0.020 inch)
Gap	Spark plug gap (14-24 kW)	0.040	in (1.02 mm)
Gap	Spark plug gap (14–24 kW)	0.040	in (1.02 mm)	cold
Gap	Spark plug gap (16/20/22 kW)	0.040	in (1.02 mm)
Gap	Spark plug gap (410 cc, 7 kW)	0.030	inch
Gap	Spark plug gap (530 cc, 10 kW)	0.030	inch
Gap	Spark plug gap (7 kW)	0.76	mm (0.030 inch)
Gap	Spark plug gap (8/10 kW)	0.76	mm
Gap	Spark plug gap (9 kW)	0.020	in (0.508 mm)
Gap	Spark plug gap (990 cc, 13-16 kW)	0.040	inch
Gap	Spark plug gap 10kW	0.030 inch	inch
Gap	Spark plug gap 13/14/15/16/17kW	0.040 inch	inch
Gap	Spark plug gap 20kW	0.030 inch	inch
Gap	Spark plug gap 8kW	0.030 inch	inch
Gap	Écartement des électrodes des bougies d'allumage	0.508	mm (0,020 po)
Gap	Écartement des électrodes des bougies d'allumage	0.76	mm (0,030 po)
Gap	Écartement des électrodes des bougies d'allumage	1.02	mm (0,040 po)
Other	Battery state of charge	1.260 or higher	specific gravity	Hydrometer test
Other	Cold Smart Start fixed temperature	20 F (-7 C)	F (C)	22-26 kW
Other	Cold Smart Start fixed temperature	50 F (10 C)	F (C)	10-20 kW
Other	Compression Ratio GH-410	8.6:1
Other	Compression Ratio GT-530	9.5:1
Other	Compression Ratio GT-990	9.5:1
Other	Compression Ratio GT-999	9.5:1
Other	Compression difference between cylinders shall not exceed	25	percent
Other	Compression difference maximum between cylinders	25 percent	percent

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

Fluid	Grade	Standard	Ambient	Capacity	Notes
Coolant	50 percent soft water and 50 percent ethylene glycol base anti-freeze	low silicate anti-freeze		2.0 U.S. gallons	Do not use chromate base rust inhibitor or high silicate anti-freeze boosters.
Engine oil		API Service Class SJ, SL or better		1.9 Qts	Engine crankcase oil capacity including filter, approximately
Engine oil	10W-30	API Service Class SJ, SL or better			For expected operating temperatures between 40 °F and -10 °F
Engine oil	30 weight organic oil (factory fill)				Units run and tested at factory prior to shipping, no break-in required
Engine oil	5W-20				Aceite 5W-20 propiedad de Generac para uso continuo, después del período de asentamiento de 25 horas.
Engine oil	5W-20 (Generac proprietary)	API Service Class SJ, SL, or better		1.03 L	Oil capacity including filter. Use for continuous use after the 25 hour break-in period; specifically formulated for gaseous powered Generac generators. Do not use special additives. Change every year or 100 hours in cold weather (below 40 F) or continuous hot weather (above 85 F).
Engine oil	5W-30	Aceite orgánico 5W-30 (la unidad se entrega de fábrica llena con este aceite)			Compruebe el nivel de aceite y, de ser necesario, añada la cantidad apropiada con la viscosidad correcta. No llene en exceso. Consulte 'Recomendaciones para el aceite de motor' para tipo/viscosidad.
Engine oil	5W-30 (factory fill) / 5W-20 GEO (continuous)	Generac proprietary gaseous engine oil (GEO)			Unit comes filled with 5W-30 organic oil; after 25 hour break-in use 5W-20 GEO
Engine oil	Above 40°F: SAE 30 or SAE 10W-30; Below 40°F: synthetic 5W-20 or 5W-30	API service classification SF or SG		1.5 Qts	With filter change = 1.5 Qts; without filter change = 1.2 Qts. Do not use SAE 10W-40. No special additives.
Engine oil	SAE 10W-30 or SAE 30	API SF or SG		1.5 Qts w/ filter change (1.2 Qts w/o)	Above 40°F
Engine oil	SAE 30	API Service Class SJ, SL or better			For expected operating temperatures above 32 °F
Engine oil	SAE 30 above 32°F; 10W-30 between 40°F and -10°F; Synthetic 5W-30 10°F and below	API Service Class SJ, SL or better; use no special additives		1.5 Qts	Oil capacity including filter
Engine oil	SAE 40 above 86 F; SAE 30 32-85 F; SAE 20W below 32 F; SAE 10W-30 all seasons	API Service SC, SD, SE or SF		3.0 U.S. quarts	Liquid-cooled 1.2 liter engine with filter change; 2.5 U.S. quarts without filter change.
Engine oil	SAE 5W-20/5W-30	API Service class SG, SH, or SJ	below -7°C		Below 20° F (-7° C)
Engine oil	SAE 5W-30 Synthetic	API Service Class SG, SH or SJ		1.7 Qts	All season; organic break-in oil required before using synthetic oil; unit is supplied with break-in oil
Engine oil	SAE 5W-30 Synthetic (all season)	API Service Class SG, SH or SJ		1.5 Qts	Organic break-in oil required before using synthetic oil; unit is supplied with break-in oil
Engine oil	SAE 5W-30 sintético	API SJ, SL o mejor		1.03 l	9 kW; no usar aditivos especiales
Engine oil	SAE 5W-30 synthetic; SAE 30 above 60 F; SAE 10W-30 20-59 F; SAE 5W-20/5W-30 below 20 F	API Service SF, SF/CC, or SF/CD		1.5 U.S. quarts	Air-cooled V-Twin engine crankcase capacity about 1.5 U.S. quarts. Oil makeup tank capacity about 2.5 U.S. quarts on Model 9067.
Engine oil	SAE 5W-30 synthétique	API classe de service SJ, SL ou supérieure			Huile SAE 5W-30 synthétique pour toutes les plages de température. N'utilisez aucun additif spécial.
Engine oil	Synthetic 5W-20 or 5W-30	API SF or SG		1.5 Qts w/ filter change (1.2 Qts w/o)	Below 40°F
Engine oil	Synthetic 5W-30	API Service Class SJ, SL or better			For expected operating temperatures 10 °F and below
Engine oil	Synthetic SAE 5W-30	API Service Class SJ, SL, or better			Synthetic SAE 5W-30 for all temperature ranges. Do not use special additives. Capacities incl. filter: approx. 1.1 qt (1.03 L) 9 kW; approx. 1.7 qt (1.6 L) 11 kW; approx. 1.9 qt (1.8 L) 16/20/22 kW.
Engine oil	SAE 10W-30	API Service class SG, SH, or SJ	-7°C to 15°C		20° to 59° F (-7° to 15° C)
Fuel		Gas natural: contenido de BTU de por lo menos 1000 BTU/ft3 (37,26 MJ/m3). Gas LP: por lo menos 2500 BTU/ft3 (93,15 MJ/m3)		250.0 gal (946 l)	Tamaño mínimo del tanque de LP es 250 gal (946 l), salvo que los cálculos de la unidad indiquen uno mayor. Solo sistema de extracción de vapor para LP.
Fuel	Gas natural	mínimo 1000 BTU por pie cúbico (37.26 megajulios por metro cúbico)			Reducciones típicas de gas natural 10-20 % respecto a LP
Fuel	Gaz naturel			37.26 mégajoules par mètre cube (1 000 BTU par pied cube) minimum	Teneur en BTU minimale du gaz naturel.
Fuel	Gaz naturel d'au moins 37,26 mégajoules par mètre cube (1 000 BTU par pied cube)	NFPA 54
Fuel	Gaz propane liquide (gazeux)			93.15 mégajoules par mètre cube (2 500 BTU par pied cube) minimum	Capacité de réservoir de gaz propane liquide minimum recommandée de 946 litres (250 gallons).
Fuel	Gaz propane liquide d'au moins 93,15 mégajoules par mètre cube (2 500 BTU par pied cube)	NFPA 58 / ICC IFGC			Réservoir de gaz propane liquide d'une capacité minimale de 946 litres (250 gallons).
Fuel	LP (vapor)	mínimo 2500 BTU por pie cúbico (93.15 megajulios por metro cúbico)		946.0 l	Se recomienda tanque de LP de 250 gal. (946 l) de tamaño mínimo si se convierte de NG a LP

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Fault codes

Code	Name	Meaning	Severity	Action
AUXILIARY SHUTDOWN	Auxiliary Shutdown	Unit will not start	Shutdown	Set auxiliary shutdown switch(es) to CLOSED (I); clear alarm
BATERÍA BAJA	BATERÍA BAJA	Indicador LED amarillo encendido en cualquier estado.	Warning	Borre la alarma. Navegue hasta BATTERY MENU del MAIN MENU para revisar la batería. Si indica GOOD, comuníquese con un IASD. Si indica CHECK BATTERY, reemplace la batería.
BATTERY PROBLEM	Battery Problem	Yellow LED illuminated	Warning	Contact servicing dealer
Battery Problem	Battery Fault	Battery condition poor or battery charger issue	Warning	Inspect battery condition and connections. Contact IASD if needed.
CARGADOR SIN CA	CARGADOR SIN CA	Indicador LED amarillo encendido en cualquier estado.	Warning	Comuníquese con un IASD.
CHARGER MISSING AC	Charger Missing AC	Yellow LED illuminated in any state	Warning	Contact an IASD
CHARGER WARNING	Charger Warning	Yellow LED illuminated	Warning	Contact servicing dealer
Controller Fault	Control Module Failure	Internal controller fault detected	Shutdown	Contact IASD for assistance
CONTROLLER FAULT	Controller Fault	Alarm message listed on controller menu.	Shutdown	Contact an IASD.
DESCONEXIÓN AUXILIAR	DESCONEXIÓN AUXILIAR	La unidad no arranca.	Shutdown	Coloque los interruptores de desconexión auxiliar en posición CERRADA (I).
EMERGENCY STOP	Emergency Stop	Alarm message listed on controller menu.	Shutdown	Check emergency shutdown switch and reset.
EXERCISE SET ERROR	Exercise Set Error	Exercise timer setting error	Warning
Exercise Set Error	Exercise Set Error	Warning; displayed if the exercise period becomes corrupted	Warning	Reset the exercise period to clear
EXERCISER NOT SET	Exerciser not set	Indicates the exercise timer has not been set.	Info	Set the exercise timer per Section 3.6.
FUEL PRESSURE	Fuel Pressure	Fuel pressure warning	Warning
FUSE PROBLEM	Fuse Problem	Unit will not start in AUTO with utility loss	Warning	Check 7.5amp fuse, replace with ATO 7.5Amp fuse if bad
High Engine Temperature	High Engine Temperature	Shutdown alarm, auto reset; 10 second delay on start-up and 1 second delay before shutdown; contacts close if temperature exceeds approximately 144 °C (293 °F)	Shutdown	Auto reset when condition clears and restart engine if a valid start signal is present
HIGH TEMP.	High temperature	High temperature switch contacts close if temperature exceeds approximately 140 C (284 F).	Shutdown	Allow unit to cool; generator restarts and LED resets once temperature returns to a safe level.
HIGH TEMPERATURE	High Temperature	Unit shuts down during operation	Shutdown	Check ventilation around generator, intake, exhaust and rear of generator
High Temperature	Overheat	Engine operating temperature too high	Shutdown	Inspect ventilation around generator, intake, exhaust, and rear. Ensure no obstructions present.
INSPECCIONE LA BATERÍA	INSPECCIONE LA BATERÍA	Indicador LED amarillo encendido en cualquier estado.	Warning	Inspeccione la batería. Presione ENTER para borrar.
INSPECT BATTERY	Inspect Battery	Battery inspection reminder	Info	Inspect battery; press ENTER to clear.
INTERNAL FAULT	Internal Fault	Internal controller fault	Shutdown	Contact servicing dealer.
Internal Fault	Internal Fault	Shutdown alarm; this alarm cannot be cleared	Shutdown	Call service dealer
LOW BATTERY	Low Battery	Yellow LED illuminated	Warning	Clear alarm; check battery via control panel BATTERY MENU; if GOOD contact dealer, else replace battery
Low Battery	Battery Voltage Low	Starting battery voltage below acceptable level	Warning	Inspect battery and battery cables. Charge or replace battery if necessary.
LOW OIL	Low oil pressure	Low oil pressure switch contacts close when oil pressure drops below the 8 psi range.	Shutdown	Add oil; turn AUTO/OFF/MANUAL switch to OFF and then back to AUTO.
LOW OIL PRESSURE	Low Oil Pressure	Unit will not start in AUTO with utility loss	Shutdown	Check oil level / add oil per Owners Manual
Low Oil Pressure	Low Oil Level or Pressure	Insufficient oil pressure in engine	Shutdown	Check engine oil level and top up if necessary. Contact IASD if problem persists.
LOW VOLTS REMOVE LOAD	Low Volts Remove Load	Unit will not start in AUTO with utility loss	Shutdown	Clear alarm and remove household loads, put back in AUTO and restart
Maintenance Message	Maintenance Message	Maintenance alert; displayed when a maintenance period expires	Info	Press Enter to confirm reset; clears the alert and resets maintenance counters
MISWIRE	Miswire	Unit will not start in AUTO with utility loss	Shutdown	Contact servicing dealer
NO UTILITY SENSE	No utility sense	Flashing LEDs indicate utility sense voltage is not connected or is below 168 volts AC.	Info	Verify utility sense voltage connection.
NOT ACTIVATED	Not Activated	Unit will not start in AUTO with utility loss	Warning	Refer to activation section in owners manual
OVER CRANK	Overcrank	Unit cranks and rests for a preset time limit then stops cranking when it cannot start.	Shutdown	Set AUTO/OFF/MANUAL switch to OFF and back to AUTO to reset the control board.
Over Crank	Over Crank	Shutdown alarm; occurs if the engine has not started within the specified crank cycle	Shutdown	Reset the control board and restart up to two more times if necessary
OVER SPEED	Overspeed	Protection shuts the unit down if it runs faster than the preset limit.	Shutdown	Contact the nearest Authorized Dealer.
Over Speed	Over Speed	Shutdown alarm; 4320 RPM for three (3) seconds or 4500 RPM immediately	Shutdown	Contact the nearest Dealer if this failure occurs
OVER VOLTAGE	Over Voltage	Overvoltage alarm	Shutdown	Contact servicing dealer.
OVERCRANK	Overcrank	Unit will not start in AUTO with utility loss	Shutdown	Check fuel line shutoff valve ON, clear alarm, attempt manual start
Overcrank	Extended Cranking	Engine failing to start after extended crank attempts	Shutdown	Check fuel supply, spark plugs, and fuel system. Contact IASD for further diagnosis.
Overload	Overload Detected	Electrical load exceeds generator capacity	Shutdown	Remove household electrical loads from generator
OVERLOAD REMOVE LOAD	Overload Remove Load	Unit shuts down during operation	Shutdown	Clear alarm, remove household loads, put back in AUTO and restart
OVERLOAD WARNING	Aviso de sobrecarga	Aviso de sobrecarga.	Warning	Remova as cargas domésticas do gerador.
OVERSPEED	Overspeed	Unit will not start in AUTO with utility loss	Shutdown	Contact servicing dealer
Overspeed	RPM Overspeed	Engine running at excessive RPM	Shutdown	Contact IASD for assistance
OVERVOLTAGE	Overvoltage	Unit will not start in AUTO with utility loss	Shutdown	Contact servicing dealer
Overvoltage	Output Voltage High	Generator voltage exceeding nominal rating	Shutdown	Reduce electrical load and restart. Contact IASD if issue persists.
PROBLEMA DE BATERÍA	PROBLEMA DE BATERÍA	Indicador LED amarillo encendido en cualquier estado.	Warning	Comuníquese con un IASD.
RPM SENSE LOSS	RPM Sense Loss	Unit was running and shuts down, attempts to restart	Shutdown	Clear alarm, remove household loads, put back in AUTO and restart; may be fuel issue, contact servicing dealer
RPM Sense Loss	RPM Sense Loss	Shutdown alarm; if no valid RPM signal within three (3) seconds during cranking, or lost for one (1) second while running	Shutdown	Control board shuts down, waits 15 seconds, then re-cranks; may re-crank once more before latching out
RPM Sensor Loss	RPM Signal Loss	RPM sensor signal not detected	Shutdown	Contact IASD for assistance
SERVICE A	Service A	Yellow LED illuminated, maintenance due	Info	Perform SERVICE A maintenance, hit ENTER to clear
SERVICE B	Service B	Yellow LED illuminated, maintenance due	Info	Perform SERVICE B maintenance, hit ENTER to clear
SHUTDOWN SWITCH	Shutdown Switch	Unit will not start. Flashing red LED.	Shutdown	Check emergency shutdown switches. Set switch(es) to CLOSED (I). Clear alarm.
STEPPER OVER CURRENT	Stepper Over Current	Stepper motor over current	Shutdown	Contact servicing dealer.
STEPPER OVERCURRENT	Stepper Overcurrent	Unit will not start in AUTO with utility loss	Shutdown	Contact servicing dealer
UNDER VOLTAGE	Under Voltage	Undervoltage alarm	Shutdown	Contact servicing dealer.
Under-frequency	Under-frequency	Shutdown alarm; if generator stays under frequency for more than 30 seconds; setting is 50 Hz	Shutdown	Check generator output
UNDERSPEED	Underspeed	Unit will not start in AUTO with utility loss	Shutdown	Contact servicing dealer
Underspeed	Engine Speed Too Low	Engine RPM below nominal specification	Shutdown	Contact IASD for assistance
UNDERVOLTAGE	Undervoltage	Unit will not start in AUTO with utility loss	Shutdown	Contact servicing dealer
Undervoltage	Output Voltage Low	Generator voltage below nominal rating	Shutdown	Reduce electrical load and restart. Contact IASD if issue persists.
USB WARNING	Aviso de USB	Aviso relacionado ao dispositivo USB.	Warning	Tente novamente com USB de melhor qualidade. Os nomes dos ficheiros no USB não podem ter mais de 8 caracteres.
Wiring Error	Electrical Wiring Fault	Wiring configuration error detected	Shutdown	Contact IASD for assistance
WIRING ERROR	Wiring Error / Miswire	Controller wiring error	Shutdown	Contact servicing dealer.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

Adjust Valve Clearance adjustment

⚠ Allow engine to cool before adjusting valve clearance.

Tools: feeler gauge, 10 mm wrench, 13 mm wrench, 14 mm wrench, 8 mm wrench, 10 mm Allen wrench, torque wrench

Make sure piston is at TDC of compression stroke (both valves closed).
Remove spark plug wire(s) and position away from plugs.
Remove spark plug(s).
Remove the four screws attaching valve cover; remove and discard gasket.
Loosen rocker jam nut (10 mm wrench 9-11 kW; 13 mm wrench 16-22 kW).
Turn pivot ball stud (14 mm wrench 9 kW; 8 mm wrench 11 kW; 10 mm Allen 16-22 kW) while checking clearance with feeler gauge.
Hold rocker arm jam nut in place as pivot ball stud is turned.
When clearance correct, hold pivot ball stud and tighten rocker arm jam nut to torque spec.
Recheck valve clearance after tightening jam nut.
Install new valve cover gasket.
Install valve cover; tighten fasteners in cross pattern to torque spec.
Install spark plugs and torque to 18 ft-lbs (25 Nm).
Reattach spark plug wire to spark plug.
Repeat process for other cylinder if necessary.

Adjust ignition magneto air gap — V-twin adjustment

Tools: 0.008-0.012 inch thickness gauge

Rotate flywheel until magnet is under module laminations.
Place 0.008-0.012 inch (0.20-0.30mm) thickness gauge between magnet and laminations.
Loosen mounting screws and let magnet pull magneto against gauge.
Tighten both mounting screws.
Rotate flywheel to remove thickness gauge.
Repeat for second magneto.

Adjusting GH-410/GT-530/990/999 Valve Clearance adjustment

⚠ The engine should be cool before checking.

Tools: Feeler gauge, 10mm allen wrench, Socket wrench

Remove spark plug wires and position wires away from plugs.
Remove spark plugs.
Make sure the piston is at Top Dead Center (TDC) of its compression stroke.
Make sure the engine is at 60 to 80 F.
Remove the four screws attaching the valve cover.
Loosen the rocker jam nut.
Use a 10mm allen wrench to turn the pivot ball stud while checking clearance between the rocker arm and valve stem with a feeler gauge.
When valve clearance is correct, hold the pivot ball stud in place and tighten the rocker arm jam nut to 174 in/lbs torque.
Recheck valve clearance.
Install new valve cover gasket and re-attach the valve cover.
Install spark plugs and re-attach the spark plug wire.
On the GT-530 and GT-990/999, repeat the process for the other cylinder.

Adjusting GH-410/GT-990 Valve Clearance adjustment

⚠ Hold the rocker arm jam nut in place as you turn the pivot ball stud.

Tools: #2 or #3 Phillips screwdriver, 10mm allen wrench, feeler gauge, socket wrench

Make sure the engine is at room temperature.
Remove the spark plug wire from the spark plug.
Remove the four screws attaching the valve cover.
Set the piston at Top Dead Center of its compression stroke.
Loosen the rocker jam nut; turn the pivot ball stud; check clearance with a feeler gauge.
Tighten the rocker arm jam nut to 174 in/lbs.
Install a new valve cover gasket and re-attach the valve cover.
Re-attach the spark plug wire; on GT-990 repeat for the other cylinder.

Adjusting GT-530/990/999 Valve Clearance adjustment

⚠ Check after first six months of operation

Tools: 10mm allen wrench, feeler gauge, torque wrench

Engine should be cool before checking
Remove spark plug wires and spark plugs
Rotate flywheel nut clockwise to bring piston to TDC of compression stroke
Ensure engine is at 60-80°F
Remove the four screws attaching the valve cover
Loosen rocker jam nut, turn pivot ball stud with 10mm allen wrench while checking clearance with feeler gauge
Set clearance to 0.002-0.004 inch (0.05-0.1mm)
Tighten rocker arm jam nut to 174 in/lbs torque while holding pivot ball stud
Recheck valve clearance
Install new valve cover gasket and re-attach valve cover
Install spark plugs and re-attach wires
Repeat for other cylinder

Adjusting GT-990 Valve Clearance adjustment

Tools: #2 or #3 phillips screwdriver, 10mm allen wrench, feeler gauge

Make sure engine is at room temperature between 60 and 80 F.
Make sure the spark plug(s) are removed.
Remove the four valve cover screws with a #2 or #3 Phillips screwdriver.
Rotate the engine by hand to bring the piston to Top Dead Center of its compression stroke.
Loosen the rocker jam nut.
Turn the pivot ball stud with a 10 mm allen wrench while checking clearance with a feeler gauge.
Hold the pivot ball stud and tighten the rocker arm jam nut; recheck clearance.
Install new valve cover gasket and re-attach valve cover.
Re-attach the spark plug wire.
Repeat the process for the other cylinder.

Adjusting Magneto Flywheel Gap adjustment

⚠ Air gap between ignition magneto and flywheel on single cylinder engines is not adjustable.

Tools: 0.008-0.012 inch thickness gauge

Rotate the flywheel until the magnet is under the module (armature) laminations.
Place a 0.008-0.012 inch (0.20-0.30mm) thickness gauge between flywheel magnet and module laminations.
Loosen the mounting screws and let the magnet pull the magneto down against the thickness gauge.
Tighten both mounting screws.
To remove the thickness gauge, rotate the flywheel.
Repeat the above procedure for the second magneto.

Adjusting Valve Clearance adjustment

⚠ Risk of Burn. Allow the engine to cool before performing the following procedure.

Tools: Feeler gauge, 10 mm wrench, 13 mm wrench, 14 mm wrench, 10 mm hex key

Allow engine to cool before adjusting valve clearance.
Remove spark plug wire(s) away from plugs and remove spark plug(s).
Remove the four screws attaching the valve cover; remove and discard gasket.
Verify piston is at TDC of its compression stroke (both valves closed).
Loosen rocker jam nut using a 10 mm wrench (10 kW) or 13 mm wrench (20–22 kW).
Turn pivot ball stud with a 14 mm wrench (10 kW) or 10 mm hex key (20–22 kW) while checking clearance with a feeler gauge.
Hold pivot ball stud and tighten rocker arm jam nut to specification.
After tightening jam nut, verify valve clearance did not change.
Install new valve cover gasket and valve cover; tighten fasteners in a cross pattern.
Install spark plugs and tighten to 18 ft-lbs (25 Nm).
Attach spark plug wire to spark plug.
Repeat process for other cylinder if equipped.

Adjusting Valve Clearance GH-410/GT-530/990/999 adjustment

⚠ Check valve clearance after first six (6) months of operation.

Tools: 10mm allen wrench, Feeler gauge, Socket and socket wrench

Engine should be cool before checking; clearance 0.002-0.004 inch needs no adjustment.
Remove spark plug wires and spark plugs.
Set piston at Top Dead Center of its compression stroke.
Remove four screws attaching the valve cover.
Loosen rocker jam nut; turn pivot ball stud with 10mm allen wrench.
Set clearance to 0.002-0.004 inch (0.05-0.1 mm).
Hold pivot ball stud and tighten jam nut to 174 in/lbs torque.
Install new valve cover gasket and re-attach valve cover.

Adjusting the Fuel Regulator (Natural Gas Only) adjustment

⚠ Avoid overspeeding the engine.

Tools: Frequency meter

Turn off utility power to the main distribution panel.
Allow the generator to start; confirm no-load frequency (roof open, door off) is 63-63.5 Hz.
Transfer load to emergency circuits and fully load the generator.
Connect a frequency meter to the output lugs of the main line circuit breaker.
Slowly turn the adjustment screws one at a time until the highest frequency is read.
When maximum frequency is reached, turn both adjustment screws 1/4 turn clockwise.
Turn utility power back on and allow the generator to shut down.

Adjusting the Fuel Regulator - 7kW (Natural Gas Only) adjustment

⚠ Do not make any unnecessary adjustments. Factory settings are correct for most applications.

Tools: frequency meter

Start the generator; let it stabilize and warm up at no-load.
Connect a frequency meter across the generator's AC output leads.
Turn the primary adjust screw to obtain a frequency reading.

Adjusting the Regulator (Natural Gas Only) adjustment

⚠ Do not remove any of the set pins.

⚠ Be careful to avoid overspeeding the engine.

Tools: frequency meter

Turn off utility power to the main distribution panel.
Allow the generator to start; confirm no load frequency is 63-63.5 Hz.
Transfer load to emergency circuits and fully load the generator.
Connect a frequency meter to the output lugs of the main line circuit breaker.
Slowly turn the adjustment screws one at a time until the highest frequency is read.
Turn both adjustment screws 1/4 turn counterclockwise.
Turn utility power back on and allow the generator to shut down.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
		0 – c.c. (-)	NOIR no 3	Fil de mise à la terre normal; obligatoire si jumelé à un commutateur de transfert de gestion intelligente de l'alimentation de Generac.
		23	BLANCO Núm. 5	Cable de señal lógica del control de transferencia
		23 (White #5)	E	Transfer Control Signal Wire
		Control system interconnections	N1, N2, 0, 15B, 23	Can be run in same conduit as AC power if length < 35 feet and all wiring rated 600V
		Generator control wiring - 1-115 ft (1-35 m)	N1, N2, T1, 23, 194	No. 18 AWG
		Generator control wiring - 116-185 ft (36-56 m)	N1, N2, T1, 23, 194	No. 16 AWG
		Generator control wiring - 186-295 ft (57-89 m)	N1, N2, T1, 23, 194	No. 14 AWG
		Generator control wiring - 296-460 ft (90-140 m)	N1, N2, T1, 23, 194	No. 12 AWG
		Longueur de fil 1 à 35 m (1 à 115 pi)	Calibre 18 AWG	Conducteurs en cuivre seulement.
		Longueur de fil 35 à 56 m (115 à 185 pi)	Calibre 16 AWG	Conducteurs en cuivre seulement.
		Longueur de fil 56 à 89 m (185 à 295 pi)	Calibre 14 AWG	Conducteurs en cuivre seulement.
		Longueur de fil 89 à 140 m (295 à 460 pi)	Calibre 12 AWG	Conducteurs en cuivre seulement.
		Neutral for battery charger	WHITE NEU/00	Must be connected to keep battery charged whether unit is running or not
	1	Connect a 2008 and later load center switch to a pre-2008 air-cooled generator: Wire 0 will not be utilized. Remove battery charger from the transfer switch. Connect N1 (BLU) to N1 (YEL), N2 (YEL) to N2 (YEL), 23 (BRN) to 23 (WHT), 194 (ORG) to 15B (RED) using UL approved wire nuts.	N1, N2, 23, 194, 15B, 0	Battery charger in transfer switch will not be utilized in operation of the generator.
	1	Connect a pre-2008 load center switch to a current or future air-cooled generator: Wire 0 will not be utilized. Connect N1 (BLU) to N1 (YEL), N2 (YEL) to N2 (YEL), 23 (BRN) to 23 (WHT), 194 (ORG) to 15B (RED) using UL approved wire nuts.	N1, N2, 23, 194, 15B, 0	Wire 194 changed to 15B on current model air-cooled generators.
0 VCC		0	NEGRO Núm. 3	CC (-) Cable común de conexión a tierra. Requerido si el generador está apareado con un interruptor de transferencia de gestión de alimentación inteligente Generac.
12 V c.c.		194 – c.c. (+)	ROUGE no 4	Pour les commandes de transfert.
12 VCC		194	ROJO núm. 4	CC (+) para los controles de transferencia
12 VDC		194 (Red #4)	D	DC (+) 12 VDC for Transfer Controls
12 VDC		DC (+) 12 VDC for transfer controls	RED 194
12 VDC		DC (-) common ground wire	BLACK 0
12 VDC		Transfer control signal wire	WHITE 23	Required if generator is paired with optional Digital Power Management (DPM) smart technology
120	1	Battery charger AC input to generator backed-up 120VAC circuit	120VAC hot, neutral	Connect via wire nuts
120 V c.a.		T1	BLEU no 3	Avec fusible 120 V c.a. pour le chargeur de la batterie; doit être branché pour que la batterie demeure chargée.
120 VAC		Fused 120 VAC for battery charger	BLUE T1	Must be connected to keep battery charged whether unit is running or not
120 VAC		T1 (White #3)	B	Fused 120VAC for Battery Charger
120 VCA		T1	AZUL Núm. 3	Con fusible para el cargador de baterías (debe estar conectado para mantener la batería cargada, esté o no funcionando la unidad)
120/208	3	parallel wye	S1 through S12; bolted junctions: 4,5,6,10,11,12 to Neutral (00); S1 and S7 to Line E1; S2 and S8 to Line E2; S3 and S9 to Line E3	Voltage Code B. Six coils, twelve leads brought out to AC connection panel.
120/240	1	3-wire	Leads 11 and 44 are hot; junction of Leads 22 and 33 is neutral	Voltage Code A. Stator AC power windings each supply 120 volts AC; in series they supply 240 volts AC.
120/240	1	GENERATOR (STANDBY) source power cables to ATS GENERATOR supply terminals	E1, E2	200A models

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Parts cataloged across the Generac GT990 family

238

Part #	Description	Category
0C3040	PRE-CLEANER	Air filter
0C8127	Recommended Air Filter	Air filter
0D3262	AIR FILTER ELEMENT	Air filter
0D4511	PRECLEANER, AIR	Air filter
0D9723	ELEMENT, AIR FILTER	Air filter
100-025	Air Filter	Air filter
C8127	Engine Air Cleaner/Air Filter	Air filter
0C7065	PANEL, ALTERNATOR DIVIDER	Alternator
067680	ASSY VOLTAGE REGULATOR 60HZ	Avr
083049	REGULATOR VOLTAGE	Avr
0F9719	ASSY PCB VREG AIR COOLED	Avr
0C1112	BELT,V-RIB 4LX42.5"	Belt
066386	ASSEMBLY, BRUSH HOLDER	Brush
0D6313	FILTER, FUEL	Fuel filter
021713B	CYLINDER HEAD GASKET	Gasket
076701	GASKET, CRANKCASE	Gasket
090239	GASKET, EXHAUST MANIFOLD	Gasket
0C2977	GASKET, CRANK CASE	Gasket
0C2978	GASKET, HEAD	Gasket
0C2979	GASKET, VALVE COVER	Gasket
0C3005	GASKET, BREATHER COVER	Gasket
0C3043	GASKET, MANIFOLD / PORT	Gasket
0C3150	ROCKER COVER GASKET	Gasket
0C4138	GASKET, EXHAUST PORT	Gasket
0C4647	GASKET, SOLENOID	Gasket
0C6069	GASKET, DIAPHRAGM	Gasket
0C8283	GASKET, DOOR SEAL	Gasket
0D2558	GASKET, ALTERNATOR AIR DUCT	Gasket
0D2559	GASKET, ALTERNATOR AIR DUCT	Gasket
0D4010	KIT GASKET	Gasket
0D4023	GASKET, MANIFOLD TO CARB (GT-990)	Gasket
0D4024	GASKET, CARB/AIRBOX (GT-760)	Gasket
0D4026	GASKET, CARB TO SPACER (GT-990)	Gasket
0D5282	GASKET, MANIFOLD TO CARB (GT-760)	Gasket
0D6327	GASKET, SPITBACK	Gasket
0E0572	GASKET,CARB TO INTAKE MANIFOLD	Gasket
0E0573	GASKET,CARB TO ADAPTOR	Gasket
0E1078A	GASKET, EXHAUST BASE	Gasket
030340	HOSE ¼ ID	Hose
048031C	CLAMP HOSE BAND 1/4	Hose
0C3036	HOSE, BREATHER	Hose
0C3036A	HOSE, BREATHER	Hose
0C9093	HOSE, BREATHER	Hose
0C9093A	HOSE, BREATHER	Hose
0C9806	HOSE, 3/8 I.D. X 6 LONG	Hose
0D3083	ASSEMBLY, OIL DRAIN HOSE	Hose
0E5079	HOSE, BREATHER	Hose
0F7065	3 FT HOSE RES 1/2	Hose
0F9176	HOSE 1/4 ID	Hose
070185	FILTER, OIL	Oil filter
070185B	OIL FILTER	Oil filter
070185F	Recommended Oil Filter	Oil filter
100-030	Oil Filter	Oil filter
70185	FILTER, OIL	Oil filter
021533	SET, PISTON RING 90MM	Service part / kit
022097	WASHER LOCK M6-1/4	Service part / kit
022237	WASHER LOCK 3/8	Service part / kit
022473	WASHER FLAT 1/4-M6 ZINC	Service part / kit
022511	WASHER LOCK 3/8	Service part / kit
022676	FUSE AGC-15A.	Service part / kit
028578	FUSE 10A X AGC10	Service part / kit
029451	677mm Rubber Tape 1/8 x 12"	Service part / kit
031971	BEARING #6205 2NSE C3 E SRI2 S	Service part / kit
0388050AE0	CABLE, #6 40" BLACK BATTERY	Service part / kit
043790A	BARBED EL 90 3/8NPT X 3/8 VS	Service part / kit
049451	BELT (POLY V 4L)-40"	Service part / kit
049721	SCREW HHC M6-1.0 X 35 G8.8 BLK	Service part / kit
052857	NUT LOCK FLANGE M6-1.0	Service part / kit
0536210209	ASSEMBLY, WIRE	Service part / kit
056147	BOLT ROTOR HHCS 5/16"-24 X 13-1/2" G5	Service part / kit
056482	BEARING	Service part / kit
065795	BATTERY CHARGER RECTIFIER	Service part / kit
066849B	SCREW HHTT M5-0.8 X 8mm	Service part / kit
071980	PIN PISTON D20	Service part / kit
071983	RETAINER, PISTON PIN 20	Service part / kit
072694	STUD, ROCKER ARM PIVOT	Service part / kit
073159	BEARING	Service part / kit
073590A	FUSE 5A X BUSS	Service part / kit
073591	FUSE HOLDER	Service part / kit
074908	SCREW HHTT M5-0.8 X 10 BP	Service part / kit
075207	CIRCUIT BREAKER 20A	Service part / kit
075207A	CIRCUIT BREAKER 30A	Service part / kit
078699E	SLEEVE, SEAMED DOWEL 10 DIA.	Service part / kit
080270	VALVE, PLASTIC TANK	Service part / kit
082121C	CLIP-J VINYL COAT .625 ID	Service part / kit
083897	TAPPET, SOLID	Service part / kit
086515	KEEPER, VALVE SPRING	Service part / kit
086516	VALVE, EXHAUST	Service part / kit
087680	NUT WING M6-1.0	Service part / kit
090388	SCREW HHTT M6-1.0 X 12 ZINC	Service part / kit
093064	ASSEMBLY, OIL FILL CAP	Service part / kit
093873	WASHER, LOCK RIB M6	Service part / kit
099727	FUSE 5A X AGC5	Service part / kit
0A1801	ASSEMBLY, BATTERY CHARGER ENGINE	Service part / kit
0A9611	FUSE 7.5A	Service part / kit
0C2229	VALVE, INTAKE	Service part / kit
0C2237	XFRSW HSB 100A 2P 250V	Service part / kit
0C2417A	EARTH STRAP 3/8X 3/8	Service part / kit
0C2967	PISTON, LC	Service part / kit
0C2969	ASSEMBLY, CONNECTING ROD (GT-990)	Service part / kit
0C2976	SCREW HHFC M8-1.25 X 65	Service part / kit
0C2981	ROCKER, COVER	Service part / kit
0C3003	SEPARATOR, OIL BREATHER	Service part / kit
0C3006	SCREW, HHFC M10-1.5 X 55	Service part / kit
0C3009	SPRING, OIL RELIEF	Service part / kit
0C3010	BALL, 1/2D OIL RELIEF	Service part / kit
0C3011	COVER, OIL RELIEF	Service part / kit
0C3026	COOLER, OIL	Service part / kit
0C3168	WASHER LOCK SPECIAL 5/16	Service part / kit
0C4680	PLUNGER, LP REGULATOR ASSEMBLY	Service part / kit
0C4706	DIAPHRAGM, TWIN REGULATOR	Service part / kit
0C4739	SCREW PPHM M3-0.5 X 6	Service part / kit
0C5313	SCREEN, OIL PICKUP	Service part / kit
0C5315	GEROTOR, OUTER	Service part / kit
0C5371	WASHER, VALVE SPRING	Service part / kit
0C5372	ASSEMBLY, BREATHER	Service part / kit
0C5729	ASSEMBLY, CRANKCASE HOUSING WITH SLEEVE	Service part / kit
0C5731	ASSEMBLY, HOUSING COVER WITH SLEEVE	Service part / kit
0C5760A	JET, GN 410 ENGINE LP (7KW)	Service part / kit
0C5760G	JET, GT990 NAT GAS	Service part / kit
0C5760J	JET, GN 410 ENGINE LP	Service part / kit
0C5764	SPRING, REGULATOR	Service part / kit
0C5765	SOLENOID, TWIN REGULATOR	Service part / kit
0C6043A	CARRIER, REAR BEARING	Service part / kit
0C6070	SPRING-SOLENOID PLUNGER	Service part / kit
0C6140	ASSEMBLY, ENCLOSURE BASE	Service part / kit
0C6735	SUPPORT, ROOF FOLDING	Service part / kit
0C6934	ADAPTOR, ENGINE	Service part / kit
0C7038B	BRACKET, ENGINE MOUNTING	Service part / kit
0C7038C	BRACKET, ALTERNATOR MOUNTING	Service part / kit
0C7061	ENCLOSURE, FRONT	Service part / kit
0C7062	ENCLOSURE, EXHAUST SIDE	Service part / kit
0C7063	ENCLOSURE, SIDE & BACK	Service part / kit
0C7064	ENCLOSURE, ROOF	Service part / kit
0C7758	RUBBER MOUNT	Service part / kit
0C8096	FAN, 8" CURVED BLADE	Service part / kit
0C8101A	PANEL, MUFFLER BOX SIDE	Service part / kit
0C8101B	COVER, MUFFLER BOX	Service part / kit
0C8284A	FOAM, BACK ENCLOSURE	Service part / kit
0C8284B	FOAM, ROOF ENCLOSURE	Service part / kit
0C8284C	FOAM, FRONT ENCLOSURE	Service part / kit
0C8285	BRACKET, BATTERY SUPPORT	Service part / kit
0C8526	CARBURETOR (GT-990)	Service part / kit
0C8566	SCREW HHFC M6-1.0 X 20 G8.8	Service part / kit
0C8808	HOOK, LIFTING	Service part / kit
0C8860	PANEL, MUFFLER BASE	Service part / kit
0C9593	MUFFLER	Service part / kit
0C9934H	ROTOR	Service part / kit
0C9935H	STATOR	Service part / kit
0D1004E	CIRCUIT BREAKER 50A 400V 2POLE	Service part / kit
0D1128	PANEL, ENGINE DIVIDER	Service part / kit
0D1606	HOUSING, FAN	Service part / kit
0D1839	BRACKET, TOP SUPPORT	Service part / kit
0D1840	BRACKET, BOTTOM SUPPORT	Service part / kit
0D1847	BOLT STATOR HHCS M8-1.25 x 305mm	Service part / kit
0D2157	SCREW SHC M6-1.0 X 50 C8.8	Service part / kit
0D2274	RETAINER, VALVE SPRING	Service part / kit
0D22850SRV	KIT, FUEL TANK	Service part / kit
0D2495	10" PNEUM WHEEL 3/4" AXLE (12.5 kW)	Service part / kit
0D2774B	BASE, AIRBOX	Service part / kit
0D2775	COVER, AIRBOX	Service part / kit
0D2930	VALVE, SUMMER / WINTER	Service part / kit
0D3220	TAIL PIPE, MUFFLER	Service part / kit
0D3867	SPRING, VALVE	Service part / kit
0D3998	NUT HEX M8-1.0 G8 YEL CHR	Service part / kit
0D4012	KIT BREATHER ASSEMBLY	Service part / kit
0D4015	KIT OIL RELIEF	Service part / kit
0D4040E	ASSEMBLY, CRANKSHAFT HORIZONTAL DIRECT DRIVE (GT-990)	Service part / kit
0D4041	ASSEMBLY, CAMSHAFT & GEAR	Service part / kit
0D4183	ADAPTOR, SPIT BACK	Service part / kit
0D4409	ELECTRONIC GOVERNOR / IDLE CONTROLLER	Service part / kit
0D4522	CONTROLLER ASSEMBLY	Service part / kit
0D4570	CAP, FUEL WITH GAUGE & VENT	Service part / kit
0D4575	BATTERY U1	Service part / kit
0D4612	SNORKEL, AIR INTAKE	Service part / kit
0D4788	PLUG STD PIPE 3/8 STEEL SQ HD	Service part / kit
0D4804	TRANSFORMER, IDLE CURRENT	Service part / kit
0D4966	OUTLET 20A 120V GFCI	Service part / kit
0D4969	OUTLET 50A 125/250V	Service part / kit
0D5014A	KNOB, AIRBOX 17mm	Service part / kit
0D5014B	KNOB, AIRBOX 95MM	Service part / kit
0D5125	SPRING, WINTER/SUMMER VALVE	Service part / kit
0D5133	SPARK ARRESTOR SCREEN	Service part / kit
0D5133A	RETAINER, SPARK ARREST SCREEN	Service part / kit
0D5269	ROCKER, COVER	Service part / kit
0D5313	ROCKER ARM	Service part / kit
0D5698A	JET IDLE PRIMER PHILLIPS HD	Service part / kit
0D6007	KIT PISTON & RINGS	Service part / kit
0D6008	KIT GEAR COVER	Service part / kit
0D6020	STUD M6-1.0 X 73	Service part / kit
0D6021	STUD, METRIC	Service part / kit
0D6024	PLATE, PUSH ROD GUIDE	Service part / kit
0D6143	TUBE, HEAT RISER 50.8 I.D.	Service part / kit
0D7668	12.3" PNEUM WHEEL 3/4" AXLE (15 kW)	Service part / kit
0D8067A	ASSEMBLY, HEAD #1	Service part / kit
0D8067B	ASSEMBLY, HEAD #2	Service part / kit
0D8675A	KIT HEAD ASSEMBLY CYLINDER 1	Service part / kit
0D8675B	KIT HEAD ASSEMBLY CYLINDER 2	Service part / kit
0D9852	ASSEMBLY IGNITION COIL	Service part / kit
0D9853D	PUSHROD, 147	Service part / kit
0E1010A	JET, GT990 LP GAS	Service part / kit
0E3372B	SEPARATOR, OIL BREATHER	Service part / kit
0E4244	BAFFLE, INTAKE	Service part / kit
0E6098	SCREEN, OIL PICKUP	Service part / kit
0E7886E	CB 50A 2P 240V S BQ2 LB (11KW)	Service part / kit
0F1338A	ASSY, IGN COIL W/DIODE NO ADV	Service part / kit
0F1338B	ASSY, IGN COIL W/DIODE NO ADV	Service part / kit
0F5022	SOLENOID COIL, 12VDC	Service part / kit
0F9035	CARBURETOR (GT-990)	Service part / kit
0C2995	GEROTOR, INNER	Pump
0C2996	GEROTOR, OUTER	Pump
0C4147	PUMP, IMPULSE	Pump
0D4123	ASSEMBLY, OIL PUMP	Pump
0D4123A	ASSEMBLY, OIL PUMP	Pump
0F6263	PULSE, IMPULSE	Pump
072655	SEAL, 35 I.D. CRANKSHAFT	Seal
078672	SEAL, VALVE STEM D7	Seal
097934	O-RING, CHECK VALVE	Seal
0C2993	SEAL, GOVERNOR SHAFT	Seal
0C3007	SEAL, 42 I.D. CRANKSHAFT	Seal
0C3008	SEAL, 38 I.D. CRANKSHAFT	Seal
0C5943	SEAL, OIL PASSAGE	Seal
0C6066	SEAL, INLET REGULATOR	Seal
0CL3007	SEAL, 42 I.D. CRANKSHAFT	Seal
0E6884	SEAL, ALTERNATOR SHAFT	Seal
0E9842	SEAL, 42 I.D. CRANKSHAFT	Seal
0E9843	SEAL, 38 I.D. CRANKSHAFT	Seal
075281	SWITCH, HIGH TEMPERATURE	Sensor
099236	Switch Oil Pressure Switch 8 PSI 1 Pole	Sensor
0A8584	Switch	Sensor
0C3025	SWITCH, OIL PRESS	Sensor
0E1497	SWITCH, OIL HIGH TEMP	Sensor
072347	SPARK PLUG	Spark plug
0D4529	SPARKPLUG	Spark plug
0E7585	SPARK PLUG	Spark plug
RC12YC	Recommended Spark Plug	Spark plug
RC14YC	Recommended Spark Plug	Spark plug
RC14YCA	Recommended Spark Plug	Spark plug

Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.

Aftermarket parts that fit this engine

A0000501971 FridayParts $109.99 0G3224TA FridayParts $29.99 0G3224TB FridayParts $29.99 FP-XP-0033262

Parts listed by aftermarket suppliers as fitting this engine — leads compiled from supplier catalogs; verify the exact part for your serial number.

Common questions

What is the oil capacity of the Generac GT-990?

The Generac GT-990 engine has an oil capacity of 1.5 liters.

What is the displacement of the Generac GT-990?

The Generac GT-990 has a displacement of 0.992 liters with 2 cylinders.

Which generators use the Generac GT-990 engine?

The Generac GT-990 powers 4 generator set(s), including Generac 8.1 GN, Generac Model 004666, Generac Model 005011, Power Systems GT-990.

How often should you change the oil in the Generac GT-990?

The Generac GT-990 oil change interval is every 150 hours.

What is a common problem with the Generac GT-990 engine?

A commonly reported issue on generators using the Generac GT-990 is: Unit will not start in AUTO with utility loss. Fix: Refer to activation section in owners manual..

Generac GT-990 Engine

Engine specifications

Generator sets powered by this engine

Troubleshooting

Fault codes

Symptoms & remedies

Common problems

Maintenance schedule

Repair guides

Service intervals

Service specifications

Recommended fluids

Fault codes

Procedures

Voltage reconnection

Parts cataloged across the Generac GT990 family

Aftermarket parts that fit this engine

Common questions