High idle speed.

[JimmyC]

I was balancing the carbs on my. Friends truck yesterday and could not get the airflow down on one of his carbs. Even with the idle screw backed out until it did not touch there was a lot of air going down the carb and the idle was fast. Cold start device was all the way off. It was like something else was holding the throttle open a bit. Any ideas?

[ChickenPinz]

Have you tried popping off the two linkage arms, one to each carb, that connect to the accelerator pedal? That'll eliminate a lot of mechanism which could cause your issue. I'd start with that.

[JimmyC]

Yes. Should have mentioned that. I was setting the idle with the linkage disconnected then adjusted the linkage not to disrupt the balance. The linkage is not the problem. Also tried disconnecting accelerator pump linkage.

[Texas710]

There is a gasket under the idle adjustment (small round piece that moves when you pull the "choke" out). That small round piece is notorious for getting a warp in it, check to make sure it's flat, and make sure the gasket is in good standing. This causes lot's of carb issues.

Also, check the float level of the carbs. This is not easy to do, lots of bolting and unbolting, but it's very important to get that set right. It can be done without the tool, but that makes it much easier, would recommend picking one up, if you haven't.

[David Dunn]

Check the butterfly shafts for play at the bushings. Spray carburetor cleaner or WD-40 at the shafts where they go through the carburetor body. If the RPM goes up that is your leak. Remember that these trucks in many cases are 50 years old and have gone through a lot of wear.

The float level would be the second place to check as mentioned above, and then the fuel enrichment system. It is a misnomer that these carburetors have a choke system, but rather a fuel enrichment system that adds more gasoline into the carburetor when it's cold rather than choking the air off, which is basically enriching the fuel also.