Cummins/Onan — Carburetor Mixture Screw Adjustment (Gasoline)
Adjustments
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Forcing the mixture adjustment screws tight will damage the needle and seat.
Procedure
- Turn both mixture screws in until lightly seated.
- Turn the idle mixture screw out one full turn.
- Turn the main mixture screw out 1-1/4 full turns.
- Start engine and run about 10 minutes.
- Apply full load and adjust governor speed nut to obtain 59 +/- 2 Hz.
- Turn main adjustment screw inward then outward to the point of highest voltage/frequency.
- Remove load and set governor speed nut to 62 +/- 1 Hz.
- Adjust idle screw for smooth operation without hunting; install limiter caps.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Full load 59 +/- 2 Hz
- No load 62 +/- 1 Hz
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.