Cummins/Onan — Field Adjustment - Carburetor
Adjustments
From a Cummins/Onan operator's manual covering: G-1710, G-495, G-743, G-855, GTA-1710, GTA-743, GTA-855. Check it applies to your exact model before use.
Applies to: Cummins/Onan G-855
Before you start
- Do not operate Thermac in full open position; re-position to minimum of 10 turns from full open.
Procedure
- Close main gas supply valve.
- Set power mixture adjustment valve at center of 'R' and 'L' marks (G-495 only).
- Close idle adjustment; open two and one-half turns.
- Attach water manometers between line regulator and Thermac, and at Thermac.
- Install vacuum gauge or mercury manometer at intake manifold.
- Open main line gas supply valve.
- Adjust line gas pressure to Thermac to 10 inches water.
- Start engine; adjust Thermac to 3 to 6 inches water; operate at rated RPM and load; adjust power mixture for highest vacuum.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- line pressure to Thermac 10 inches H2O
- Thermac to carburetor 5 inches H2O
- maximum main outlet setting 20 inches H2O with engine shut down
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.