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Old 10-05-2010, 07:55 PM
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Holley Help!

Just installed a freshly rebuilt holley 750 vac advanceon my 84 C-10. Its on a 350, mild cam, headers, airgap intake, timing is dead on. My question is that when I start it it will idle fine it seems, but when I give it gas it will seem as some cylindrs on the passenger side weren't firing and all of a sudden pick up and fire. I adjusted the drivers side airfuel screw in to see if it would respond and the engine did infact die. The passenger side has no effect. Could I have an idle passage possibly blocked causing the passenger side of carb to not supply enough fuel at idle? Its like it smooths out and they all fire when I pass the idle cicuit at about 1500 rpms. Thanks
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Old 10-05-2010, 07:57 PM
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Check your timing again and adjust it to where it doesn't do that any more.
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Old 10-05-2010, 08:10 PM
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What is the idle timing? Whats the vacuum reading at idle (manifold)?

Any vacuum leaks? Spray WD40 or carb cleaner around the base of the carb at idle and see if rpm changes at all. Thats a leak at the baseplate. Check all hoses. Got your vac ports on the carb plugged or used? Is there a ported vac line in the front of the carb not being used (tiny like 1/4" round nipple)

If the idle mixture screws (even just 1) have no effect you might have a faulty or incorrect power valve which will feed fuel randomly at idle. Do you know what power valve it has (stock is 6.5)

If an idle passage was blocked it should just sputter and stall. Itd be the same as screwing the idle mixture screw all the way in.

How about the air bleed holes on the top of the carb. There are 2 tiny ones and 2 large. The tiny are air for the idle mixture. So tiny like a pin hole. DONT enlarge them but try to blast em with carb cleaner or air. Sometimes crud gets in there and gives screwy idle.

The fact that its rebuilt probably means its any of the above.
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Old 10-05-2010, 08:57 PM
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Fold an old bath towel so that you have a square that will fit down over the carburetor air horn and cover it well. Remove the air cleaner stud. Have a buddy fire the motor up. Bring the r's up to whatever you can tolerate without making you crazy, maybe 4500-5000. Have your buddy turn the key off and mat the loud pedal at the same time you slam the towel down hard onto the top of the carb and hold it there until the crank stops turning.

This is one of those "good ole boys" tuneups for the carb circuits. Most times it works. Sometimes not.

The motor will be flooded with fuel, so mat the pedal to let lots of air in when you try to re-start it.
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Old 10-05-2010, 09:59 PM
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Quote:
Originally Posted by techinspector1
Fold an old bath towel so that you have a square that will fit down over the carburetor air horn and cover it well. Remove the air cleaner stud. Have a buddy fire the motor up. Bring the r's up to whatever you can tolerate without making you crazy, maybe 4500-5000. Have your buddy turn the key off and mat the loud pedal at the same time you slam the towel down hard onto the top of the carb and hold it there until the crank stops turning.

This is one of those "good ole boys" tuneups for the carb circuits. Most times it works. Sometimes not.

The motor will be flooded with fuel, so mat the pedal to let lots of air in when you try to re-start it.

Funny to hear someone mention this. We used to use a carb storage cover for that purpose. We had one with a hole dead center and slid it down over the filter stud. It was a better seal than the shop rag trick.
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Old 10-06-2010, 09:17 PM
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I've done this numerous times- but w/o shutting the engine off. Run the revs up real good, slap a rag over the mouth of the carb w/the throttle still open wide, until the r's drop way back down then remove the rag so the engine catches. Never even had a backfire, despite what you might expect.
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Old 10-06-2010, 09:27 PM
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Quote:
Originally Posted by cobalt327
I've done this numerous times- but w/o shutting the engine off. Run the revs up real good, slap a rag over the mouth of the carb w/the throttle still open wide, until the r's drop way back down then remove the rag so the engine catches. Never even had a backfire, despite what you might expect.
I did the same thing but just slammed the choke plate closed with my finger . As cobalt said. Never had a backfire so I wasn't afraid of getting burnt .
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Old 10-07-2010, 09:36 AM
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Quote:
Originally Posted by techinspector1
Fold an old bath towel so that you have a square that will fit down over the carburetor air horn and cover it well. Remove the air cleaner stud. Have a buddy fire the motor up. Bring the r's up to whatever you can tolerate without making you crazy, maybe 4500-5000. Have your buddy turn the key off and mat the loud pedal at the same time you slam the towel down hard onto the top of the carb and hold it there until the crank stops turning.

This is one of those "good ole boys" tuneups for the carb circuits. Most times it works. Sometimes not.

The motor will be flooded with fuel, so mat the pedal to let lots of air in when you try to re-start it.


Too funny! We had a similar trick we used to call a "California carburetor kit" (usually performed on the side of the highway). We would simply get rpms up a bit and then pinch off a rubber fuel line with a pair of pliers untill the engine dies. Sometimes it works, sometimes it dont! The idea is to flush debris out of the needle and seat and/or circuts.


I concur that it is probably a "one sided" carburetor issue.
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Old 10-07-2010, 09:46 AM
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You know, this is a situation that using a can of spray carb cleaner might just help.

Follow the can directions, you might get lucky. You're only out a couple bucks at worst.

PS- keep it out of your eyes! The engine will be running for at least part of the cleaning operation, so watch out for what the fan blows around, keep it off of your paint.
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