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Old 03-11-2010, 12:00 PM
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backfire through carb please help

my chevy 350 ran great before i installed an edelbrock manifold on it

It stumbles off idle and if you give it gas it backfires through the carb.
To install the HEI distibutor i bump the engine around to feel it push out air, but i feel air both times, but one time is more forceful than the other so i removed the valve cover and made sure both valves were closed. i also put a compression gauge on and one stroke pushes oiut 30 psi and the next stroke pushes out 60 psi. so i chose the 60 psi stoke. when the air pushes out the timing mark is about 12 o clock.
After i feel the air push out i bump it a little more to get the timing mark at zero on the timing tab, i can usually get it pretty close. Then i stab in the distributor so rotor is pointing at about 5:30 pointing to number one post on the cap and vacuum anvance is pointing to #6. firing order is 18436572 with accel wires. I've done this several times. My timing light is lighting and i see the mark is under the tab, the tab is painted so i don't know exactly where it's at, i can see zero and all the dash marks, it's about 3 marks before zero right now. Carb is holley 80457-3, I've taken it apart and cleaned it with gumout carb cleaner, put new gaskets in. I've checked for vacuum leaks and didn't find any. I adjusted float level so it's just under the sight plugs. I replaced the power valve three times. I actually installed the manifold twice with new gaskets to make sure there were no leaks.

What am i doing wrong? i'm really frustrated, please help

one more thing, the fast idle screw is backed out all the way, i don't see how it works because there is a red plastic lever that pushes it open and the choke push rod is mounted under that, if i tighen the fast idle screw the red lever pushes the choke closed rendering my electric choke inoperable

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Last edited by KingKil33; 03-11-2010 at 01:44 PM.
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Old 03-11-2010, 06:00 PM
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take a can of carb cleaner and spray around where the gaskets are to find the intake leak. It sounds like you have a vacuum leak somewhere.
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Old 03-12-2010, 01:05 PM
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Thanks for the reply, i went out today and bought carb studs and a new gasket (i was using bolts). After i put that on i sprayed carb cleaner along both sides of the intake and around the base of the carb. I didn't notice any change in idle. I checked all the intake bolts to make sure they were tight, i found one that turned a little more, but it still backfires when i git it a lot of gas. I appreciate your help you got any more ideas? I'td be nice if there were someone in the dayton ohio area willing to come look at it.
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Old 03-12-2010, 02:08 PM
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the carb cleaner just pooled and sat until it dried
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Old 03-12-2010, 05:20 PM
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where do you have your timing set?
What springs/weights in the ditributor?
Are you unplugging and capping the vacume advance when you time it?
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Old 03-12-2010, 05:46 PM
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My timing light is lighting and i see the mark is under the tab, the tab is painted so i don't know exactly where it's at, i can see zero and all the dash marks, it's about 3 marks before zero right now. The stock springs and weights.
No. It won't stay running when i unplug the vacuum advance and plug the port.
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Old 03-12-2010, 05:52 PM
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Scratch the tab off so you can see the timing marks so then you can time it correctly. You say you took apart the carb, have you done any adjustment to it? air fuel mix could be off need tweeking alittle or the floats are out of adjustment, are you are sure it is time now? JMO


Cole
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Old 03-12-2010, 08:17 PM
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i adkusted the floats so the level is just under the sight plugs, i screwed in the mixture screws till it almost dies then back them out 1 turn
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Old 03-12-2010, 08:27 PM
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Quote:
Originally Posted by KingKil33
i adkusted the floats so the level is just under the sight plugs, i screwed in the mixture screws till it almost dies then back them out 1 turn
Did the engine smooth out when you brought it out one turn? Did youdo this while it was running?


Cole
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Old 03-14-2010, 11:47 AM
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yes, i made the adjustments while it was running and it sounds smooth until i give it gas
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Old 03-14-2010, 12:00 PM
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Quote:
and it sounds smooth until i give it gas
Ayuh,... For whatever Reason,... It sounds like it goin' Lean...

Might have something to do with gettin' things Close enough...

Quote:
Originally Posted by KingKil33
After i feel the air push out i bump it a little more to get the timing mark at zero on the timing tab, i can usually get it pretty close.
What am i doing wrong? i'm really frustrated, please help
In Mechanicin',... Close Enough Never is,...
That's Why Specs are printed for about Every aspect of the things We work on...
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Old 03-14-2010, 12:03 PM
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double and triple check your plug wires. sounds alot like mixed up wires, and it is easy to do when reinstalling dizzy.
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