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Briggs powered Cub won't idle down

4342 Views 4 Replies 3 Participants Last post by  tomw0
Briggs 16.5 horse.
Model 312777
Type 0150-E1
Code 990414ZO

This is on a Cub Cadet 1600 belonging to a fellow I work with. Throttles up and runs fine, then won't idle back down. We're figuring there is a butterfly return spring or something that isn't hooked up quite right. There is one small spring that doesn't seem to do anything; might be the one hooked up wrong. Can anybody post up a picture of diagram of the governor & carb linkage?

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There should be a throttle return spring that is tensioned when the control is moved to FAST or rabbit setting. The spring should pull the throttle wide open when the engine is not running. The governor should pull the throttle closed or towards 'closed' whenever the engine is running.
If the governor arm is not connected to the throttle bellcrank, the governor will not affect rpms, and the engine can over-rev enough to turn it into scrap metal.
The governor fights the control-tensioned spring, the balance between them will change the 'set point' or throttle position, i.e., how far the throttle plate is open. With full control tension, the governor should close the throttle plate under no or low load, and then allow the control spring to open the throttle wide when you have more load. If the rpms increase as the load eases, the governor should start to pull the throttle plate in the closed direction.
So, in short, you have a spring, and a hard link. Spring to the throttle control, and hard link back to the governor. Read the manual and adjust the governor, a three-step process: loosen the clamp, rotate the internal shaft, tighten the clamp. That will set the governor to remove all 'slack' internally, so when the engine fires, the governor arm will be pulled back by the 'spool' moving it, pulling the throttle plate 'closed', to prevent runaway. If it doesn't, after adjustment, then you may have a governor that has come loose or is damaged internal to the crankcase.
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