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Discussion Starter · #1 ·
OK I recently had some choke problems as most of you probably noticed, but got that fixed. The choke opens up about 3/16" till good and warm. Anyhow, now there's a slightly different problem.

Every once and a while (2 out of 5 maybe) when I suddenly mash the pedal down at idle, the engine revs up perfect but either pops a wee bit of fire back through the carb or pops out the exaust. Timing is dead on perfect so I know that's now it. At idle the engine runs perfect and if you ease on the pedal there's no problem, but any time you mash it real quick and cause the butterflies to open, it pops back a little. It's nothing major and doesn't even effect it running, but I'm worried about it popping back through my air cleaner.

Any ideas? I can't adjust the mixture screws since they're sealed on this carb, and it's suppose to be auto-adjusted.
 

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Sloe Lurner
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accelerator pump??

what carb are you running?? sounds like your accelerator isnt doing it's job. you might be leaning out too much too quick. Are you running stock fuel pump or elec?? filter?? vacum or mech advance??
 

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Discussion Starter · #3 ·
Stock QJet, electric pump at 4PSI, filters are clean, vac and mech advance. This thing was running absolutely perfectly before. You could sit there and rev it all day without a problem. But now it sounds like it's lean like you said.

I checked the accelerator, it's doing it's job. The choke's opening like it should so I don't have much more to go by. It just started doing this after I set the choke to be 3/16" closed when cold and 3/4 to full open once warm.
 

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Hotrodders.com Moderator
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Accelerator pump or possibly to lean on the idle mixture screws. If the choke is now working properly, any of the adjstments you did before to the carb may need to be revisited. Is the engine completly warmed up when it is popping.

How much vacuum do you have at Idle
 

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Discussion Starter · #6 ·
I don't think the accelerator pump's bad since it worked just 5 minutes before I fixed the choke problem. I'll give it a look tomorrow though.

The mixture screws were my first thought, but I can't turn them since they're capped over on this QJet. The popping happens after the engine is warmed up. While it's still cold and the choke is closed I can do anything I want and it responds perfectly.

The reason I'm running on 4PSI is because it's what the computer at Autozone showed as the max seat pressure of the float bowl needle. It's not adjustable though. It's not running low before the carb, the clear filter is full to the brim.
 

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I am just going to guess at this one but is the spring on the airvalve door still working right? Over time that spring can get weaker and allow the door to open as time goes by and require a slight increase in tension adjustment. Its pretty easy to adjust, a allen wrench and screw driver. If its broken I can tell you how to make a new one without monkeying around with the torsion spring that is on there now. Think about it though. Most QJets don't have a secondary accelerator pump but some do have the accelerator discharge holes that give an enrichment when the secondary "throttle" plates are opened like you are doing when you stab the throttle. Now I cant remember if those holes, not the tubes, were above or below the air valve door. Any ways, when you stab the throttle both the primary and secondary throttle plates stand on end and if that spring weakened you could get a lean condition until fuel is drawn from the secondary fuel discharge tubes and or the accelerator holes. Look at what you got and let us know.
 

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Discussion Starter · #8 ·
Ok it's been a while since I posted in this topic since I seemed to have gotten it fixed. Well it idles fine now when cold, but it's definitely running rich. Even when the choke is fully opened the exaust smells real bad and it back fires and pops when you get on the pedal real hard. Any clues? I'd just tweak the mixture screws but they're sealed and my pop forbids me to take it off and open them. :boxing:
 
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