Faint stumble

[Doober]

So I'm up in Michigan for a few days, and I've driven the Malibu some. What I've noticed is a faint stumble just above idle. I had the same issue before and it wound up being one of the vacuum port plugs on the carb was cracked. This time around nothing is cracked, so I'm a little confused. Disconnected/cleaned out/blew out the air orifices on the carb, no luck. Moved the accelerator pump to the other 2 possible positions (Edelbrock 1405), no luck. It's just barely above idle, around 1,000-1,200rpm. Once I get the throttle past a certain point RPMs jump up at least 3-400, and past that the car runs fine. I'll only be up here a few more days & it's not a huge thing, but it's definitely something I need to address. The car sat for several months, but was started occasionally. I don't think it's an old/bad gas issue, but I'm not positive.

Any suggestions?

 

[Ed Cannon]

Try backing out your mixture screws a half turn and reset the idle.

 

[Robert1320]

And check the acc pump. The umbrella may be getting weak or hard.

 

[Doober]

Check the pump? I'm guessing this involves removing the top portion of the body? I'm not sure I'll be able to get that involved with the carb (flying out Friday and don't want to leave a car that doesn't run at all). I'll mess with the mixture screws some more tomorrow. I originally started at somewhere around 1¾ turns and backed them out from there, but honestly it didn't seem to help the idle at all (tried to lean it out a little but it didn't do much). I'm starting to wonder if the carb is finally ready for a rebuild, I don't know its history before it came into the junkyard about 8 years ago, but I'm guessing it was just a bolt-on-and-go deal.

 

[Robert1320]

You'll need some gaskets to into the pump.