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Discussion Starter · #1 ·
I'm going to open one up tomorrow off an 81 vette 350 for a customer, What is the most likely culprit to clog the the main idle circuits? The customers son have rebuilt it once with Chem dip and the works, and it ran great for about 65 miles then it took a crap.

The car starts and runs magnificently when the choke is closed, but as soon as the butterflies open it dies deader than a door knob.

So what should I look for other than clogged main idle circuits in a Quadrajunk?
 

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I'd be looking external of the carb--deteriorating fuel lines and crap in the tank. Put a good fuel filter on it. Look for sources of vacuum leaks/warpage that may occur when the motor is hot. Then rebuild the carb and it should be good to go.
 

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Discussion Starter · #4 ·
Not Hot, no vacuum leaks, If you start it, it's running GREAT, perfect as far as a Chevy is concerned, but manually open the primary choke flap and purrrrrrr.... it simply stops running as the fuel is used up the farther the flap opens the less it runs.

I am sure it's a clog in the metering circuits, I just wanted thoughts prior to removal. Thanks guys, this is my first Quadra junk tune in about 9 years....
 

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Man, it's been forever since I've worked on a QuadraCrap. Actually a good carb. If it idles fine when warmed and choke off, then it's likely the enrichment circuit. They call it a power piston, and it raises the metering rods out of the jets to richen when your throttle-up. Equivalent to a Holley accel pump, but at lower vac like a power valve. Anyway, the springs can be rusted soft or broken, killing the enrichment circuit. There are some other little things they have like fuel tubes and bore plugs that can be fueling issues. As Dennis said, a visual inspection outside and then inside would be my first move.

If the issue is at idle (and you don't find obvious idle circuit issues), check the secondary metering rod well plugs. If there is no sealer or the sealer is bad, re-seal them with epoxy.

David
 

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Discussion Starter · #6 ·
You see it's too lean to idle, if you start it cold it's perfect, if you start it hot it's perfect. BUT, ONLY if you hold the choke flap closed... So I'm fairly certain it's a clog as it ran perfect for so many miles then all of the sudden took t not running at all with the choke flap open unless you were pumping the throttle a LOT...


Thanks for the advice, will look into it here in about 20 minutes.
 

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First of all check to be sure they used the correct thick wooden type base gasket when they put it back on. Secondly, this sounds like a power piston/ metering rod issue as well. 3rd, when you turn the Quad over you will see epoxy on the plugs the main jet well is plugged with. If you dont, you need to reseal it there because they do leak after you shut the car off. It causes hard starts after you have driven a ways. Check and make sure the carb top gasket wasnt torn when the youngins rebuilt the thing too and of course verify they didnt bump the float when reassembled. I have done a BUNCH of Quads, still do a few, but have always liked the carb. They are just like anything else, if you dont know all the tricks then you will not get the result you want. They have been wrongfully given a bad rep.
 

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You see it's too lean to idle, if you start it cold it's perfect, if you start it hot it's perfect. BUT, ONLY if you hold the choke flap closed... So I'm fairly certain it's a clog as it ran perfect for so many miles then all of the sudden took t not running at all with the choke flap open unless you were pumping the throttle a LOT...


Thanks for the advice, will look into it here in about 20 minutes.
The idle tube restrictions are most likely clogged. You need to pull the top off the carb. You can try and use a piece of thin wire to clear them but the surest way is to pull them. Its a bit of a chore but doable.
 
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