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Old 05-19-2008, 06:20 PM
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Very rich idle

I recently swaped intake manifolds changing from a Victor Jr. to a Weiand Stealth Air-strike. I picked up about 5 inches of mercury at idle going from ~11inHg to ~16inHg. Ever since this however the car idles very rich, to the point that it is blowing lots of smoke out the exhaust and causing eyes to burn.
I have tried adjusting the mixtures screws and they are set about 3/4 turns from bottoming out. Any further lean and the car doesn't run well. The transfer slots are set to the appropriate .02 inch but the primarys can be completely closed and the car will still idle great at 1000 rpm. It has great throttle response and runs very well other than the fact that it is so rich. The spark plugs have around 1 hour of run time on them and they look like charcoal. I don't know what is so wrong, it ran great before the manifold swap and I wouldn't think that picking up a little manifold vacuum would cause that many problems. What do you think could be wrong?

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Old 05-19-2008, 06:23 PM
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If it's a Holley, could be a ruptured power valve. Did you get any hiccup or backfire after the change?
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Old 05-19-2008, 06:34 PM
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check to make sure nothing is holding the secondarys open a small amount.

sam-missle
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Old 05-19-2008, 06:36 PM
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I did put in a new power valve and that didn't change it at all. I don't think the secondaries are being held open but that would explain the high idle. Also I can plug the boosters in the venturies with my fingers and there is no change so the main circuit is not being activated.
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Old 05-20-2008, 12:45 AM
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what kind of carb, if its not a good match to your motor you may need to decrease the size of the idle channel restrictors(installing a small v shaped wire in the metering block) or enlarge the air bleeds (drilling the main body). Messing around with these things if you dont know what you're doing is a good way to ruin a carb, i recommend getting a good holley tuning book (SA designs has a real good one) and reading up on it.

air bleeds ( the larger ones are for the idle, and the smaller ones are for the main metering system)


idle feed restrictors
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Old 05-20-2008, 03:57 PM
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Its a Speed Demon 750 mechanical secondary. I was also considering restricting the idle feed ports. It just seems strange that the increase in vacuum could cause such a problem.
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Old 05-20-2008, 04:15 PM
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Riich

Friend of mine has the same Carb on a 383 with VortecVictorJr. With the full exhaust hooked up it will choke a mule it's so rich. When he has open headers it runs perfectly clean. (Any) exhaust other than open headers and it's severely rich. I mentioned to him about restricting the Idle feed circuit with wire but he wont tried it. Guess he like choking everyone behind him.LOL!
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Old 05-21-2008, 04:41 AM
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carb

What are your initial and total timing numbers???


Keith
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Old 05-21-2008, 09:27 AM
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If the engine is idling high, most likely your primary or secondary butteflys are open too far causing this rich condition. The larger intake would have had less air velocity so you would have had to open the butterflies further to get it rich enough.

Remove the carburetor and reset the butterflies first. If you're idling too high you won't be able to set the idle mixture properly.
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Old 05-21-2008, 09:40 AM
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Quote:
Originally Posted by NovaSS350
I recently swaped intake manifolds changing from a Victor Jr. to a Weiand Stealth Air-strike. I picked up about 5 inches of mercury at idle going from ~11inHg to ~16inHg. Ever since this however the car idles very rich, to the point that it is blowing lots of smoke out the exhaust and causing eyes to burn.
I have tried adjusting the mixtures screws and they are set about 3/4 turns from bottoming out. Any further lean and the car doesn't run well. The transfer slots are set to the appropriate .02 inch but the primarys can be completely closed and the car will still idle great at 1000 rpm. It has great throttle response and runs very well other than the fact that it is so rich. The spark plugs have around 1 hour of run time on them and they look like charcoal. I don't know what is so wrong, it ran great before the manifold swap and I wouldn't think that picking up a little manifold vacuum would cause that many problems. What do you think could be wrong?
How much timing do you have in the motor at idle? How far open is the idle eze? Have you checked for any vacuum leaks both around the intake and between the carb base and the intake mounting pad?
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Old 05-21-2008, 06:37 PM
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2 quick things. 1, demon carbs are craptacular. 2, if you are pulling more vac below the carb it will...... pull more fuel. Does your demon have replacable air bleeds? Worked with a few of those carbs, had to keep an air bleed kit handy to make them decent on the street. Single plane intakes seem to work ok, but dual planes tend to pool the fuel in the plenums and lower runners with those carbs.
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Old 05-23-2008, 04:15 PM
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The issue with the timing is that I have had it advaced to the point of kicking back on the starter and retarded to the point of not running well and everywhere in between. It doesn't seem to make a difference on how rich it runs. I try to set it where I can get the highest vacuum without detonation but it still smokes.
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