Cummins/Onan — Carburetor Adjustment
Adjustments
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan NHC-NHCV engine
Before you start
- Forcing mixture adjustment screws tight will damage needle and seat. Turn in only until light tension can be felt.
Procedure
- Turn mixture screws in until lightly seated, then back out turns specified in Table 1.
- Start engine and warm thoroughly at least 10 minutes.
- Move speed control to slow position.
- Pull governor back so throttle stop screw is against stop.
- Adjust throttle stop screw to obtain 1200 rpm, or 1100 rpm if low speed screw exists.
- Set idle adjustment screw about 1/8 turn outward from midpoint of maximum speed range.
- Re-adjust throttle stop screw to specified rpm and release governor arm.
- Check main mixture by rapidly accelerating; adjust if hesitation.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Idle Mixture: 1 to 1-1/2 turns
- Main Mixture: 1-3/8 to 1-5/8 turns
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.