Give Jerry another cookie!
On manual choke carbs, the idle vent valve was introduced in mid-year 1958, and discontinued in mid-year 1960; so that really narrows the range of your carburetor. Based on that information, we can do a kit (CS-3460).
The linkage should be adjusted such that the vent is open at idle, and closes when the throttle is slightly opened. If you complete remove the "stopper", nothing changes except for a source of "dirt" entering the carburetor. The excessive idle vapors would be vented, as designed.
I agree with Jerry that this valve is not your problem.
When I suggested to change the fuel filter, I should have posted to test the fuel delivery at the carburetor. A weak fuel pump, a cracked fitting in the fuel line from the tank, or a partially clogged "sock", or even chunks of crud in the tank that might be sucked into the tube at higher RPM (higher fuel requirement), and then drop out (gravity) when the engine was turned off.
Please understand I am certainly not adverse to selling a rebuilding kit,
but I am a long way from certain that it will help.
Is there any way you could rig up a temporary fuel tank (maybe a outboard marine tank) with an electric pump to totally bypass the current fuel delivery system?
Jon
