Cummins/Onan — Adjusting High-Idle Speed
Adjustments · governor actuator
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MDKB, Cummins/Onan MDKBH
Before you start
- Keep your hands away from the engine belt and pulleys.
- The actuator could overheat if the battery is left on more than 10 minutes.
- Be prepared to clamp off supply and return fuel lines to stop the engine.
Procedure
- Adjust the speed control lever stop.
- Measure engine speed with a strobe or injector clamp-on type tachometer.
- Remove the front and top access doors and loosen the front/left side panel assembly for access to the speed adjusting screw.
- Disconnect the actuator leads and connect a 12 volt battery to the actuator terminals using a battery switch.
- Switch the battery on, start the genset, measure engine speed (rpm) and stop the engine by switching off the battery.
- Loosen the lock nuts on the two bottom screws and back out the clamping screw if speed is not between 3300 and 3400 rpm.
- To increase speed turn the speed adjusting screw in 1 turn clockwise; to decrease turn it out 1 turn counterclockwise.
- Repeat until high-idle speed is between 3300 and 3400 rpm and set the lock nut.
- Run the clamping screw in by hand until snug, back it out 1-1/2 turns and set the lock nut.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- High-idle speed 3300 to 3400 rpm
- New base initial adjustment: screw head 3/4 inch (19 mm) from the base
Full service-parts list: Cummins/Onan MDKB →, Cummins/Onan MDKBH →
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.