Cummins/Onan — Mixture Screw Adjustments
Adjustments · Carburetor
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Forcing mixture adjustment screws tight will damage needle and seat.
Procedure
- Ensure ignition system works properly and governor is correctly set.
- Use mixture settings in Table 1 as preliminary adjustments.
- Turn mixture screws in until lightly seated, then out specified number of turns.
- Start engine and allow to warm up until choke is completely open.
- Remove all electrical loads; connect voltmeter and frequency meter.
- Hold governor linkage so throttle lever rests against throttle stop screw.
- Adjust stop screw to obtain 90 to 100 volts.
- Set idle adjustment screw slightly rich from midpoint of highest voltage range.
- Release governor and apply full load. Set main adjustment screw similarly.
- Remove load and check stability; adjust governor sensitivity as necessary.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 90 to 100 volts throttle stop setting
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.