Increasing Idle speed

[ekamm]

I have a 3a and the idle speed increases as it warms up. I have to do the foot under the pedal trick to get it down which is fine before it is fully warmed up. When it's warm I can lower the idle with my foot but after releasing the pedal it creeps back up. I feel that my carbs are rich, would this be a cuase of the increase in idle speed? Or is there some thing else to look at?

 

[NutmegCT]

Eric - if you can lower the idle speed by lifting up on the pedal, then you can be pretty sure the problem is binding in the linkage. Could be anywhere, but first check the bushing where the pedal linkage goes through the firewall (to the right of the pedal).

Often that gets worn down and causes binding. Unfortunately, it's not much fun to repair.

Tom

 

[tdskip]

I think Tom's got it, and one way to confirm if if the idle increases on it's own without any change in throttle at all (sitting still, no pedal pressure or linkage movement). That is probably unlikely however....

 

[TR3driver]

To some extent, it's normal for it to idle slow when the engine is below normal operating temperature. That's why there is a fast idle cam built into the choke mechanism.

Being able to lower the idle by pulling up on the pedal could also be the throttle discs dragging on the carb throat, due to misalignment and/or worn throttle bushings. Rebushing the carbs is what mostly solved my problems with fast idle.

I also found that the balls in the pivots in the throttle linkage were worn oval. After fiddling with the linkage, I wound up with the oval balls causing it to bind only at idle.

 

[Geo Hahn]

...I also found that the balls in the pivots in the throttle linkage were worn oval. After fiddling with the linkage, I wound up with the oval balls causing it to bind only at idle.

Sometimes the ovalness can be remedied by repositioning the ball 90 degrees from where it is now. This can be done by undoing the ball and introducing a washer under it, then reinstalling with the ball ending up in a slightly different orientation than before.