Cummins/Onan — Carburetor Main and Idle Adjustment
Adjustments
From a Cummins/Onan service manual covering: 4CCK, 5CCK, 5CCK-150R, 5CCK-3CR. Check it applies to your exact model before use.
Applies to: Cummins/Onan 4CCK, Cummins/Onan 5CCK, Cummins/Onan CCK engine
Procedure
- Run engine at normal operating temperature with almost a full load connected.
- Turn main adjusting needle out about two full turns.
- Turn it slowly in until engine begins to lose power and speed.
- Turn it out very slowly until engine runs smoothly at full power and speed.
- With no load, turn idle needle in until engine loses considerable speed, then out until smooth.
Tools required
- Onan carburetor wrench (4208169) Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Do not open main needle more than 1/2 turn beyond maximum point of power
Full service-parts list: Cummins/Onan 4CCK →, Cummins/Onan 5CCK →
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.