Hello, I am new to this forum, I recently purchased a nice `74 Maverick with the 250 cid. It was running a little rough so I took it to my mechanic for a tune up. I got it back and it does idle smoother but still has some issues. When I accelerate the engine hesitates then will pick up fine. Sometimes if I don't gently feather pump the gas pedal when pulling away from a stop it will stall. I had an old VW that did this once and when I looked into it seems that the carb. has a small mechanical pump that will give an extra squirt of fuel when accelerating. As you probably guessed by now I'm not a mechanic but wonder does this 1 bbl carb, have that pump as well? I think this may be the problem. I really don't want to take it back to the mechanic as I don't think he works on these much. Rather than a carb rebuild kit I am thinking of buying a good OEM rebuilt unit and installing myself. Also this weekend I think I will replace all the vacuum hoses. Any advice? Could this also be the vacuum advance unit? I had a mustang ll that was acting this way and that was the problem with it. Also, what is the small round plastic valve in the vacuum line that leaves the vacuum advance do? Thanks in advance for any suggestions.
If it runs good other than the dead/flat spot, then yes the pump inside the carb is probably either not functioning or maybe just misadjusted... This check/test is performed with engine off... Remove the air cleaner and with choke blocked open, operate the throttle to see if it produces a little "squirt" when it's moved... It should give a squirt as soon throttle opens a small amount... Sometimes they can be out of sync and not operate till throttle is already open somewhat...
My '74 250 didn't have a spring on the accelerator pump and I experienced the same issue that you are having...along with not wanting to start after sitting for a few days. I added a spring from an old Holley I had sitting around and it fixed the problem.
