Cummins/Onan — Carburetor Main Jet and Idle Adjustment
Adjustments · Carburetor, gasoline
From a Cummins/Onan operator's manual covering: 4.0CCK, 4.0CCK-3CR, 5.0 CCK, 5.0CCK, 5.0CCK-3CR, 5.0CCK-3R. Check it applies to your exact model before use.
Applies to: Cummins/Onan 4.0CCK, Cummins/Onan CCK engine
Procedure
- Make all adjustments with the engine at normal operating temperature.
- For main jet, connect a full or nearly full load; turn main adjusting needle out about two full turns.
- Turn needle in slowly until engine begins to lose power and speed, then out slowly until engine runs smoothly at full power and speed.
- If hunting occurs, open main adjusting needle a little more (no more than 1/2 turn beyond maximum power).
- For idle jet, with no load, turn needle in until engine loses considerable speed, then out until engine runs smoothly.
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
- Float level dimension 5/16 in
Full service-parts list: Cummins/Onan 4.0CCK →
Source: Cummins/Onan operator's 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.