Hey everyone,
I've got a Q-jet on a fairly built SBC. I just re-adjusted the float to factory spec to try to cure this problem.

It idles just fine, and if I slowly give it gas, it will bring the RPMs up OK.
However, if I quickly open the throttle, it will bog.

I'm guessing it's an accelerator pump issue, so I'm going to try a new one.

I've uploaded a video to show what's going on.

http://download.yousendit.com/8439E83B2E73B515


Thanks.

 

The secondary AV tension is too loose.

Can't see in the video, but do you have the choke pull-off hooked up to the AV?

 

The AVs are being held closed by my right hand in the video. They do need to be dialed in, however. But I wouldn't imagine they're contributing being held closed, though I agree it displays similar symptoms.

The carb did not come with the complete pull-off linkeage, so it is not hooked up.

I found another accelerator pump and purchased one for my carb model (which it's apparently a 81 305 carb, by the way). One is longer than the other one. I put the new longer accelerator pump on and it seemed to help, but it still has a bit of a bog. Will the shorter accelerator pump have more of a pump shot, or is there any difference?

 

Shorter means the plunger will be higher in the cavity, and therefore should deliver a longer shot.

Make sure check valve ***** are where they should be, etc. It needs to deliver the shot immediately, any delay will bog you.

 

Thought I would update this thread in case it get searched.

It was a huge vacuum leak. Another case of drastically over-thinking things. Granted, this was a carb I just rebuilt and it was good to get the float set dead on.

But always remember to check the basics. This is like the 3rd Q-jet I've fixed recently with really big driveability problems that ended up just being a vacuum leak. Check between the carb and manifold, and between the sections of the carb. In this particular case, I'm running some spacers and they weren't sealing at all. I don't know if this is very orthodox, but I've used RTV high-temp gasket sealer the last couple times to fix this when new gaskets didn't work (because of a warped casing, I assume). If you use black RTV, it doesn't look as goofy.

Spray WD-40 or starter fluid around the base of the carb if it runs like crap and see if it idles up. If it does, you've got a vacuum leak.

So yeah...vacuum leak. Big trouble maker on Q-jets, lol.

Thanks again for the advice, guys. I ended up going with the shorter pump. I was thinking the shorter was better as well, but there was a bit of debate between my buddies and I.

 

Glad to hear you got it figured out.

You should know, however, that RTV is not for use in environments that will have prolonged exposure to gasoline or gasoline vapors. It will eventually eat the stuff.