Onan tech
Are there a Onan techs on this site ? I’ve got a 4 ky spec f that won’t move the throttle when cranking. The governor rod and gear inside are not available anywhere but they don’t look that bad. I...
Forum Discussion
I tried to find my old post about it.
With the engine not running the throttle sits at wide open. As the engine starts and speed increases the flyweights which are attached to the gov gear push on the thimble. The thimble pushes on the arm which moves the linkage and reduces engine speed. When the balance between flyweight pressure and main spring tension equalize the engine speed stabilizes. If the spring is pulled tighter the engine rpm increases. It's a balancing act between these two forces.
If more load is placed on the engine it will drop rpm and the flyweights will reduce pressure which allows the throttle linkage to open the throttle plate more which speeds up the engine to it's balance point.
When adjusting the linkage you need the gov arm to be full against the thimble which is bottomed on its shaft against the flyweights. With the gov arm in that position you want to move the throttle linkage to wide open throttle plate. While holding it in this position you then tighten the pinch bolt on the linkage arm.
You can use the hertz setting on a multi meter to adjust the gov spring tension. The governor linkage rod often has a very thin spring coiled around it with its ends attached to the arm at each end. This spring is important to help keep the slop out of the linkage rod and gov arm holes. If it's missing you can experience hunting as the the slop will allow the throttle to to speed the engine slightly and then the flyweights react and try to bring it back in balance.
I dont remember exactly what the linkage arm looks like but the main spring usually has a choice of holes which it can be placed in. Manufacturers will often say what holes it should be in. If the main spring is in the wrong holes you may get somewhat erratic rpm control or floating surge etc. Trying others holes will often hit on the right one. Dont mistake fuel problems such as surging or hunting for gov problems. Get the gov adjusted properly then move on to other issues.
If the flyweights, gear, arms and rods are not worn bad and it's adjusted properly it's then pretty bullet proof. Most problems are more likely to be fuel related.
With the engine not running the throttle sits at wide open. As the engine starts and speed increases the flyweights which are attached to the gov gear push on the thimble. The thimble pushes on the arm which moves the linkage and reduces engine speed. When the balance between flyweight pressure and main spring tension equalize the engine speed stabilizes. If the spring is pulled tighter the engine rpm increases. It's a balancing act between these two forces.
If more load is placed on the engine it will drop rpm and the flyweights will reduce pressure which allows the throttle linkage to open the throttle plate more which speeds up the engine to it's balance point.
When adjusting the linkage you need the gov arm to be full against the thimble which is bottomed on its shaft against the flyweights. With the gov arm in that position you want to move the throttle linkage to wide open throttle plate. While holding it in this position you then tighten the pinch bolt on the linkage arm.
You can use the hertz setting on a multi meter to adjust the gov spring tension. The governor linkage rod often has a very thin spring coiled around it with its ends attached to the arm at each end. This spring is important to help keep the slop out of the linkage rod and gov arm holes. If it's missing you can experience hunting as the the slop will allow the throttle to to speed the engine slightly and then the flyweights react and try to bring it back in balance.
I dont remember exactly what the linkage arm looks like but the main spring usually has a choice of holes which it can be placed in. Manufacturers will often say what holes it should be in. If the main spring is in the wrong holes you may get somewhat erratic rpm control or floating surge etc. Trying others holes will often hit on the right one. Dont mistake fuel problems such as surging or hunting for gov problems. Get the gov adjusted properly then move on to other issues.
If the flyweights, gear, arms and rods are not worn bad and it's adjusted properly it's then pretty bullet proof. Most problems are more likely to be fuel related.
