Cummins/Onan 6.3 NHEL / 6.5 NH — Carburetor Mixture Screw Adjustments - LP Gas
Adjustments · LP gas carburetor
For the Cummins/Onan 6.3 NHEL / 6.5 NH, from the Cummins/Onan service manual.
Applies to: Cummins/Onan NHEL
Before you start
- Forcing the mixture adjustment screws tight will damage the needle and seat; turn in only until tension is felt.
Procedure
- Turn mixture screws in until lightly seated for preliminary adjustment.
- Turn main adjustment screw out 2-1/2 (±1/4) turns and idle adjustment screw out 1 (±1/4) turn.
- Start engine and run about 10 minutes at light load.
- Connect voltmeter, frequency meter, and load bank; start set and apply full load; verify frequency within 59 ± 2 hertz.
- Turn main adjustment screw inward until voltage/frequency drop, then outward until they drop again; set at highest point.
- Remove load and verify frequency within 62 ± 1 hertz; adjust governor speed nut if necessary.
- Turn idle adjustment screw inward until voltage/frequency drop and engine runs rough; back out until engine runs smoothly without hunting.
- Pull governor linkage forward so throttle lever rests against throttle stop screw; adjust stop screw for 55 hertz and 100 (±4.5) volts.
- Release linkage, set voltage and frequency, adjust governor sensitivity; add and remove half load several times.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Preliminary: main screw out 2-1/2 ± 1/4 turns; idle screw out 1 ± 1/4 turn
Full service-parts list: Cummins/Onan NHEL →
Source: Cummins/Onan service 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.