need weber help

[chuck smith]

My 427 set up starts and idles well, however, one carb(actually half of one IDF,the number 2 cylinder) seems to have fuel comimg from the pump jet all the time,resulting in much fuel vapor at idle and at speed causing poor running that seems to be isolated to that one cylinder only. Do you guys have some expertise in these matters? All help appreciated. chuck

 

[Jac Mac]

There should be a small ball or needle check valve in the acc pump circuit that prevents that ( works like the needle under the shooter screw in a holley). It may have a piece of debris preventing it from seating or if the carbs have recently been worked on may have been overlooked on assy.

Jac Mac

 

[chuck smith]

are you talking about the needle valve? or pump demand valve?

 

[Jac Mac]

are you talking about the needle valve? or pump demand valve?

It should be in the pump demand valve which is the screw assy that holds the discharge nozzle in place. Its a ball bearing or similar that is inside that 'screw' that prevents fuel being pulled into the venturi at fast idle speeds but allows fuel to be drawn into the engine at high rpm/large airflow rates to help enrich at full throttle. A small piece of debris or some moisture that has created a bit of corrosion to stick the ball will be allowing fuel to flow thru that pump jet nozzle all the time.

Jac Mac

 

[chuck smith]

thanks Jac Mac, I see what you mean. I will change it out today. chuck