440 carb issue

[64Belvedere]

A buddy of mine has an old plymouth with a built 440, purple shaft cam, Holley 750 mechanical converter and 3.91 gears. Was working awesome, then gradually it had trouble idling, and then it became a pig to get it to start. It cranks over forever to start. Have to gas it to keep it running. Runs great under throttle and down the highway at speed but doesn't want to run at low RPM. I'm thinking fuel pump or dirt in the carb....Any other ideas?

 

[69RRGTX]

Do you have any way to hook up a make shift fuel pressure gauge to see how the pump is acting?

Are the idle screws set correctly? They should be around 1.5 turns out at idle (turning in or clockwise leans out the idle circuit wanting to stall the engine, turning out does the opposite.) These should be set witht he engine running.

Also does the carb have the clear sight windows in the fuel bowls? Anyways, make sure they are set at the correct level adjusting the float if need be.

If not then pick up a rebuild kit and have at it.

-Mark

 

[RedHot67]

I bet you have a vacuum leak.

Dan

 

[miller]

First thing I'd do is replace the fuel filter, and go from there.

 

[SlinktRR]

If it runs bad at idle or low rpm but great WOT, would suspect something wrong with the idle circuit. Either mixture screws not set correctly or some junk in the passages. Try tuning the idle mixture screws to get max vacuum at idle, also spray carb cleaner into the carb while running. Use compressed air on the idle screws (remove the screws and blow out the passages).

 

[WP29440SE]

as stated , get a fuel pressure gauge on it between the pump and the carb. you need 5 - 6 psi . my money is on the fuel pump.

 

[64Belvedere]

turned out to be a hole in the top of the aftermarket fuel pump. a second set of eyes spotted it while cranking. Weird stuff happens around here. Another example.

 

[SlinktRR]

A hole in the diaphragm? Once you change it out post a picture.