Cummins/Onan — Gaseous Fuel Adjustments
Adjustments · Gas mixer / fuel system
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Gaseous fuels are flammable and explosive and can cause severe personal injury or death. Keep a type ABC fire extinguisher handy.
Procedure
- Start the engine and let the set warm up under a partial load (at least 1/4 rated load).
- Disconnect all loads, shut down, connect a tachometer and disconnect the governor linkage at the carburetor.
- Start the engine and hold the throttle closed by hand so the engine does not overspeed.
- Adjust the throttle idle position screw to obtain 800 rpm; reconnect the governor linkage.
- Connect full rated load and turn the main fuel valve to full-rich.
- Slowly turn the main fuel valve toward lean until the engine begins to lose speed.
- Slowly back toward rich until the engine carries the full load smoothly.
- For dual fuel, switch to LPG by closing the manual shutoff valve in the natural gas supply line.
- Turn the LPG flow adjustment valve clockwise until the engine begins to lose speed.
- Slowly turn it back counterclockwise until the engine carries full load smoothly.
Tools required
- Tachometer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Idle speed 800 rpm
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.