Sign in to follow this  
erock194

40 Plymouth high idle

Recommended Posts

Can't get Idle to come down. Even with the linkage disconnected it won't idle lower. Original flathead. Any help would be appreciated. Thanks

Share this post


Link to post
Share on other sites

Make sure that your linkage is not too tight.  Just a little looseness will ensure it returns to the idle stop position.  Once again the voice of experience speaks.

Share this post


Link to post
Share on other sites
9 hours ago, erock194 said:

Can't get Idle to come down. Even with the linkage disconnected it won't idle lower. Original flathead. Any help would be appreciated. Thanks

Are you stuck on fast idle with the choke mechanism ?

Share this post


Link to post
Share on other sites

Advanced timing can cause faster idle. Have you checked your timing?

 

Fuel delivery to the cylinders is metered by controlling and manipulating vacuum. Air is sucked into the manifold putting vaccum pressure on various passages and orifaces in the carb , drawing fuel in. The right amount needed at various throttle positions. 

 

If your carb has vaccum leaks, or parts are missing or mis-adjusted you get incorrect fuel delivery. That can lead to uncontrollable higher RPMs. You’ve tried external carb adjustments to no improvement. 

 

What model carb? When was it last rebuilt and resealed? Where is your  air/fuel idle adjustment screw set? Choke fully opening when warm? Do you have a vacuum gauge you can use to troubleshoot?

 

History of this carb known? Proper gaskets used? 

Share this post


Link to post
Share on other sites

My '40 had the same issue, finally traced it to the butterfly shaft being so worn that I was sucking air around it.

  • Like 1

Share this post


Link to post
Share on other sites
On 8/29/2019 at 2:40 AM, Plyroadking said:

My '40 had the same issue, finally traced it to the butterfly shaft being so worn that I was sucking air around it.

 

Worn throttle throttle shaft bushes will normally show up as a cause for weak mixture, can't see that as a cause for fast idle.

Share this post


Link to post
Share on other sites

Spraying an exeternal fuel source such as carb cleaner, around the carb and base area, may help in finding air leaks. Engine RPM may rise higher yet, as the external fuel is drawn in through the leaks.  

Edited by keithb7 (see edit history)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this