idle too fast when engine is hot

ArtS

Buddy1 had a problem with too little idle RPMs when engine is cold but I've got a different issue with a fully warmed up 308 Twin H. The choke spring tension is good, snaps shut when cold, and stays partly open when engine is running and warmed up. Kick down is good after cold start and will cause idle to drop to about 1000 RPM after the engine has been running for a minute or so. My problem is that after I make a 20-30 mile trip in hot or cold weather, the idle RPM (with the Hydramatic in neutral) increases to around 1200 and pretty much stays there. This is just about the same RPM as fast idle after a cold start. Kick down does not work to reduce the RPMs. Car is drivable but engine is turning way too fast at idle in neutral. Any thoughts on how to fix this issue? ArtS

Jon B

I'll tell you what I found (but I have a pre-war car): I had the linkage adjusted too tightly. There was no play. So when I'd let up on the accelerator, the throttle couldn't return to idle. I just loosened up on it so there was a bit of play even when my foot was off the gas.

ArtS

Jon B wrote:

I'll tell you what I found (but I have a pre-war car): I had the linkage adjusted too tightly. There was no play. So when I'd let up on the accelerator, the throttle couldn't return to idle. I just loosened up on it so there was a bit of play even when my foot was off the gas.

Thanks, Jon. I'll take a look at the dual carb linkage. This seems like a possible solution to the problem since it only crops up when the engine compartment is at full operating temperature thus causing slight expansion of the various linkage components. If I take the car for a run, then let it sit and cool down for a hour or so, idle RPMs are much reduced upon start up.

Unknown

You say choke stays partly open with engine running and warmed up. It needs to be fully open when warm.

ArtS

Billy K.TN. wrote:

You say choke stays partly open with engine running and warmed up. It needs to be fully open when warm.

I'm going to have to check this out. If full open means full travel of the choke valve, I'd say its not full open. Choke valve on warm engine sits about 60 degrees from full closed. Maximum travel of the valve when I push on it is about 90 degrees. So maybe I'm running too rich?? Thanks Billy.