69 red fastback 20 Report post Posted August 22, 2015 I have a holley 4150 600 cfm and when I give some throttle it stumbles and then it will take off. My thought is the accelerator pump, but I'm not the best on carbs, any thoughts from the people on here that are carb pros would be greatly appreciated Quote Share this post Link to post Share on other sites
Regta 10 Report post Posted August 22, 2015 I think you're on the right path. first step is to see if the accelerator pump is actually working. With the engine off, and air cleaner removed, look in the top of the front barrels of the carb while with your hand moving the throttle. If the AP is working you should see a stream of gas squirting on each side. If nothing, probably the AP diaphragm is broken inside. The AP is located o the underside of the front bowl. Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted August 22, 2015 Thanks for the reply, I'll check that tomorrow and see if it is shooting gas like you said, I assume if that is the problem the AP is easy to come by Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted August 22, 2015 Well I did what Regta advised and I am getting gas when I work the throttle, so if the accelerator pump is working what else could cause the hesitation Quote Share this post Link to post Share on other sites
barnett468 418 Report post Posted August 22, 2015 . disconnect and plug your vacuum advance and leave it plugged until prob is solved. set initial timing to 10 degrees btdc. tighten distributor but make sure the bolt is not bottoming out. if you have a holley or quick fuel carb, set the gas level so it is just below the inspection windows at idle . . if you have plastic windows, they must be removed to do this. reset fuel mix screws. take timing lite with you and check timing if it happens again. Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted August 22, 2015 Thanks, I'll give it a try Quote Share this post Link to post Share on other sites
Regta 10 Report post Posted August 24, 2015 Another thing is to check any vacuum plugs to see if any are cracked or broken. I had a car stumbling and found a large plug on the back of carb had cracked allowing a large vacuum leak Quote Share this post Link to post Share on other sites
69 red fastback 20 Report post Posted August 25, 2015 Thanks for the response, I'm going to put on a carb spacer tomorrow night when I get home and then I'll check for vac leaks Quote Share this post Link to post Share on other sites