Jeff Morgan

I recently put a new Q-jet on my 86 Firebird. It bogs almost everytime that I go to WOT. I can also be cruising along at 55 or 60 MPH and go to WOT and it bogs. Will adjusting the AV help? I've did all of the tune-up stuff already.. Need Help

thanks

Jeff Morgan

dan

Try tightening the secondary air valve spring to make it open slower. This will probably reduce or cure your stumble

Ed Maher

If it's a chronic problem and you haven't messed with your AV tension the cure is NOT to tighten the AV past the stock setting.
10 to 1 one of the secondary "accelerator pump" tubes has fallen out or is clogged.
Easy test. Take off your aircleaner with the car running. Blip the throttle to full open. You should see some wetness on the AV flaps towards the front center. If you don't see it on either you're doing it wrong (or they are both bad) If you see it on one, not the other, you've found your problem. If you have access to compressed air, you can try blowing some in the little hole at the front of the flap. You could try this with carb cleaner if you don't have compressed air, though it probably woulnd't work as well, depending on the clog. If it doesn't start spraying then, you'll have to pull the airhorn and make sure it didn't fall out. You'll see the tubes when you pull it. It's pretty common for them to fall out. Drive it back in carefully. You can also put a little epoxy around it too to help.
...ed

Damon

I agree with Ed. One other thing you should check for is the secondary air valve's movement shouldl be "checked" by the little vacuum can on the passenger side of the carb. There is (should be) a little metal rod that connects the two. The diaphragm should take about 2 seconds to open from fully retracted to fully extended. It should be fully retracted while the engine is running, and then extend as soon as you shut the engine off.

Also check your air valve spring tension. It should be about 1/2 turn from the zero tension point for street performance. Push the air valve open with your finger (engine off). It should take just a few ounces of pressure to open the air valves. If it practially "falls" open then you need to tighten the air valve spring. If you need to know how to do this we can help with that, too.

One last thing- the accelerator pump. Most of the time the bog is caused by secondary problems but not always. With the engine off, choke open, try opening the throttle quickly while you look down the primary throttle bores. You should see a stream of fuel squirting out and hitting each of the booster venturis. If not, or the stream is weak or "broken" then you have accelerator pump problems and the carb needs a rebuild.


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94 Firebird Formula M6- No options but Z rated tires. No mods over $10. 13.5@105.
79 Malibu "beater" w/junkyard 400 SBC, tweaked QJet 4bbl, finally a decent set of heads, a few other tricks. A maddening 13.000001 @ 108 on the motor with little traction. No nitrous runs with the new heads yet.

"One of the last remaining QJet tuners on Planet Earth!"