Carb slide thumb test. Failed.

[John C Hannah]

So I've always heard that if you cover the big hole in the Venturi with with you thumb and let the slide come down it should fall slowly from the suction. My bike was having a hard time running and I switched it with my other carb (which passes the thumb test) and now it seems to be running.

On the carb that fails the thumb test, the diaphragm doesn't have any holes in it.

So what would cause it to fail?

 

[xschris]

The choke circuit could be leaking. Also the area around the slide where the rubber meets may be loose.