Generac — Clean/Gap/Replace Spark Plugs
Maintenance · Ignition System
From a Generac owner's manual — check it applies to your exact model before use.
Applies to: Generac 15 kW EcoGen, Generac GT-999 engine
Before you start
- Never disconnect spark plug with engine running.
- AVR charged up to 3 minutes after power down. Wait 5 minutes before removing filter housing.
- Grasp spark plug cable boot when disconnecting, not cable itself.
Parts for this job
- RC12YC Spark plug Amazon eBay $12.90 NAPA $11.52 FridayParts $19.99
Part numbers from the service-parts list for Generac 15 kW EcoGen. Verify against your serial number before ordering; some links are affiliate links.
Procedure
- Remove AVR filter housing screw from back panel.
- Remove AVR filter housing.
- Remove spark plug cables from spark plug terminals by grasping boot.
- Thoroughly clean area around spark plugs.
- Remove spark plugs using 5/8 inch spark plug socket.
- Check condition of threads in cylinder head and plugs.
- Clean spark plugs using wire brush and commercial solvent.
- Check spark plug gap using wire feeler gauge.
- Adjust gap to 1.02 mm (0.040 inch) by bending ground electrode.
- Finger tighten spark plugs into cylinder head.
- Using spark plug socket, tighten to 15-18 ft-lbs (20-25 Nm).
- Install spark plug cables onto spark plug terminals.
- Install AVR filter housing and screw to back panel, torque 50-96 in-lbs (6-11 Nm).
Tools required
- 5/8 inch spark plug socket Amazon
- Wire feeler gauge Amazon
- Wire brush Amazon
- Commercial solvent Amazon
- Spark plug socket Amazon
- Torque wrench Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Spark plug type: RC12YC Amazon eBay $12.90 NAPA $11.52 FridayParts $19.99
- Spark plug gap: 1.02 mm (0.040 inch)
- Spark plug torque: 15-18 ft-lbs (20-25 FridayParts $42.95 Nm)
- AVR filter housing torque: 50-96 in-lbs (6-11 Nm)
- Replacement interval: 1000 hours or 4 years
Full service-parts list: Generac 15 kW EcoGen →
Source: Generac owner's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.