Cummins/Onan — Carburetor Mixture Adjustment
Adjustments
From a Cummins/Onan service manual covering: 2.5 MAJB-53BR, 2.5 MAJB-53CR, 3.0 MAJB-1R. Check it applies to your exact model before use.
Applies to: Cummins/Onan MAJ, Cummins/Onan MAJB engine
Before you start
- Forcing mixture adjustment screws tight will damage the needle and seat
Procedure
- Apply a full load to the engine.
- Turn in the main fuel adjustment until engine speed drops, then turn out the needle until speed returns to normal.
- Remove the load from the engine.
- Turn the idle fuel adjustment out until speed drops slightly, then turn the needle in until speed returns to normal.
Tools required
- Carburetor adjustment wrench Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Open both needles 1 to 1-1/2 turns off their seats if engine will not run
Full service-parts list: Cummins/Onan MAJ →
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.