Cummins/Onan B43 / B48 — Carburetor Mixture Adjustment
Adjustments
For the Cummins/Onan B43 / B48, from the Cummins/Onan service manual.
Applies to: Cummins/Onan B48
Before you start
- Over-tightening mixture adjustment screw will cause carburetor damage.
Procedure
- Warm engine at least 10 minutes.
- Set throttle to slow; adjust throttle stop screw for 1000 rpm idle.
- Turn idle mixture screw in until speed drops, then out until speed drops again.
- Set screw about 1/8 turn outward from midpoint.
- Readjust throttle stop for 1000 rpm idle, then governor low speed stop for 1100 rpm idle.
- Move to fast; adjust high speed stop to recommended speed.
- Check acceleration; adjust main mixture in 1/8 turn increments if needed.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Walbro: idle 1-1/8 turns, main 1-1/2 turns
- Nikki limited idle: idle 1-1/4 turns
Full service-parts list: Cummins/Onan B48 →
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.