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post #1 of 7 (permalink) Old 06-04-2011, 11:09 PM Thread Starter
 
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spit and sputter

My 68 gto has a 2 year old edlebrock 750. Today it began surging at low idles. (When I pull up to stop signs and stop lights) Then on the way home it backfired when I goosed it in third gear. It did this twice, the surging seemed to get worse. Are these problems related, and what do I do? Thanks guys
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post #2 of 7 (permalink) Old 06-05-2011, 08:04 AM
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Sounds like a carb issue, or timing, distributor issue.

How old is the carb? Rebuild time? Your mixture screws not functioning to correct this if the dist, and timing are ok may indicate like mine did, you have internal issues in the carb.

Running rich with air mixture idle screws may be hampered with float issues or accelerator pump issues. My situation was similar to yours was corrected with a rebuild. About 35.00 for parts.

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post #3 of 7 (permalink) Old 06-05-2011, 08:57 AM Thread Starter
 
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spit and sputter

Bought carb new 2 years ago. Has 1000 on it. Never any trouble before. I installed a new cam 2 weeks ago. That is when I noticed it. My choke won't set either , are these problems related. I have it set 1 and half turns after bottoming out mixture screws, is that about right?
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post #4 of 7 (permalink) Old 06-05-2011, 12:31 PM
 
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It could be a vacuum leak around the base of the carb, and if it is popping back through the carb on hard accel it could be the intake gaskets. I had some gaskets do that years ago when I swapped intakes. Since then I use Victor or FelPro and havent had it happen since. The carb cleaner trick around the base and manifold might show it.

Surging is a lean condition, it could just be some crud in the carb, or it could be a bigger problem. One thing you can try is to remove the air filter housing, rev the engine up above idle, say to around 3000 or 3500, then cover the primary side with your hand so it creates a suction. Be careful, you can get a laceration from a high vacuum engine. When it starts to die off, move your hand and let it come back. Do that a few times, you should get black smoke from the tail pipes when you do it right. Doing that will suck all the varnish and crud from the gas out of the small passages. If that doesnt fix it then its time to pull the top and take a look.

Since you did a cam swap, my guess is a vacuum leak somewhere. That will make a lean condition real quick. The E carbs are so simple with few small passages, compared to a Qjet, that I would tend to look for leaks first.
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post #5 of 7 (permalink) Old 06-05-2011, 07:40 PM Thread Starter
 
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spitting ad sputtering

Today I took out my idle mixture screw and blew air through the holes. Took my 68 out and it is still backfiring on a hard accel and surging at off idle, I'm stuck, any thoughts? This began all of the sudden
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post #6 of 7 (permalink) Old 06-06-2011, 10:07 AM
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If your carb was rebuilt 2 years ago it may likely have been rebuilt with NON user friendly ethanol parts. If the rubber is black instead of blue this may indicate this. Perhaps the ethanol has gotten to the rubber?

When your carb was off was it turned upside down, internal parts disturbed, float not working right etc..... if was off a while did the rubber dry out? Different factors could be causing this. Your situation is similar to mine I had and a rebuild on a 3 year old rebuilt carb cured the issues.

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post #7 of 7 (permalink) Old 06-06-2011, 10:42 AM Thread Starter
 
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spit ande sputter

Thanks for the info. I think a rebuild is in my future. But I did not rebuild the carb 2 years ago, I bought it new 2 years ago. I have never had any trouble with the float or anything. I did not turn it upside down when it was off the car. It was off the car for about 2 weeks though. Thanks
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