C1 Carb wierd idle

[Don Izzo]

My 1960 has a rebuilt/ restored carb that I purchased from Chicago Corvettes about a year ago. It sat in the box until about a month ago when it was installed. I started the car last week and during a test drive I am finding that the idle will increase a few hundred RPM off idle and stick until I rev the motor. Then the RPM's will settle back Down. The motor is warmed up and The choke is working properly. I have disconnected the throttle linkage and it still does it when slowly operated by hand. I can raise the idle by hand slowly and it will hang up just off idle stop setting a few hundred RPM.. Here is the weird part. if I the kill the engine while it has hung up, the linkage will drop back down to the stop position on it's own...And it doesn't do it if the motor is not running. It seems like it's some kind of vacume thing. All the linkage is ok and not binding. If I manually operate the linkage return it will operate fine. If I increase the return spring tension the peddle gets to stiff with little idle return inprovement. Any Ideas??

Don In NY

[roy braatz]

Re: C1 Carb wierd idle

You may have the metering rod spring that is stretched to long causing the metering rods to take to long to return to it's position.But you have to take the carb top off to replace it.And or the vacuum port that pulls them down is clogged

[Don Izzo]

Re: C1 Carb wierd idle

I am going to go to a very good carb shop in NY tomorrow. This guy has a flow bench. Do you think he will be able to diagnose my problem?? I am sure if I install an addition return spring on the carb back side I will cure the symptom but not the cause.

Don in NY

[roy braatz]

Re: C1 Carb wierd idle

How can he create vacuum pull on the metering rods?

[Clem Z.]

Re: C1 Carb wierd idle

you only check the air flow on the bench not the fuel flow. barry grant and holley have a "wet flow" carb bench to check wet flow.

[Clem Z.]

Re: C1 Carb wierd idle

sounds like the shaft or base plate bore is worn. try loosening all the butterfly screws.back off the idle speed screw and recenter the butterflys in the base plate bores and retighten.