Idle mixture - Team Camaro Tech
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post #1 of 16 (permalink) Old Jul 12th, 04, 03:52 PM Thread Starter
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Which way on idle mixture screws, clockwise lean or rich?
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post #2 of 16 (permalink) Old Jul 12th, 04, 04:13 PM
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Clockwise lean on most carbs.

Some Holley carbs for emissions applications were the other way around.

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post #3 of 16 (permalink) Old Jul 12th, 04, 04:13 PM
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What kind of carb? Most are clockwise to lean them out (tighten the screw) but some holleys are the opposite.

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post #4 of 16 (permalink) Old Jul 12th, 04, 04:16 PM
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post #5 of 16 (permalink) Old Jul 12th, 04, 04:38 PM
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post #6 of 16 (permalink) Old Jul 12th, 04, 06:54 PM Thread Starter
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It's a Holley 80508 vac sec 750. Can't keep it from running rich. Transfer slot is OK. Power valve is OK (5.5 with 11" vac @idle). No vacuum leaks that I can find. Proper gap (.015) on acc pump arm. I had to open the secondaries a bit to get the main idle screw back to get the transfer slot right.
Really stumped! Electic choke unloads quickly.
Idle mix screws are 2 turns from seat for best vac.
Timing is 12 deg initial with 34 total all in by 2800 rpms. also has a Crane adj vac can and am using manifold vac for timing.
Anything that I'm missing?
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post #7 of 16 (permalink) Old Jul 13th, 04, 01:44 AM
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View down the air horn with engine at idle and see there is no fuel dribbling from the venturi.

If it is, fuel level set too high.

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post #8 of 16 (permalink) Old Jul 13th, 04, 04:42 AM
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My experience with holley carbs is 3/4 turn from seat is average, I've had a few go to 1 turn maybe 1 1/8 but never more than that... If your power valve is blown you'll idle rich and usually you'll smell fuel. Wouldn't hurt to replace it and 5.5 is fine.

As suggested make sure your floats are right at the bottom of the sight holes, then close your sec's down and seat the screw against the blades and go a 1/4 turn per holley tuning spec's. You really want them closed, the 1/4 turn is to insure they don't bind in the bore when closed.

Disconnect your vacuum advance, plug the source it was on and set your idle mixture screws to 1 1/4 turn from seat each. Fire up the engine and get it warm, set your idle and check your manifold vacuum. You should have to lean things a touch, I set it for max vacuum and usually go about an 1/8 turn lean (unless it starts to stumble). Check your idle and hook your vacuum advance back to manifold vacuum and adjust the idle back down. Don't know what cam you are running but try to set the idle around 700-800 rpm out of gear or about 600-650 or so in gear. Your transfer slot should not be uncovered too much at this point...

We have some info in the techref area that may help you too. www.camaros.net/techref/series_2.html

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post #9 of 16 (permalink) Old Jul 13th, 04, 02:21 PM Thread Starter
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Thanks For the info Dennis.
The cam I'm running is a Comp XE 274. The reason I have the secondaries open is get the car to idle with the .020 of the transfer slot showing. Without opening them, I have to set the idle screw up and then expose the transfer slot.
Doesn't seem to be any gas dripping in the carb at idle.
It runs pretty good except for fouling plugs.
The ignition is fine (HEI) and I've tried AC R44's and 45's. Gapped anywhere from .42 to
.50. Doesn't make much differance.
Got to be the carb, but I'm really stumped.
Anything else to look for?
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post #10 of 16 (permalink) Old Jul 13th, 04, 02:35 PM
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Don't worry about the transfer slot being uncovered .020", Barry Grant carbs are the only ones that recomend .020". The Holley can be fine with as much as .040" maybe more. With your cam you have no reason to open the sec's to compensate for anything...

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post #11 of 16 (permalink) Old Jul 14th, 04, 01:00 AM
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Quote:
It runs pretty good except for fouling plugs.
I'd try either a projected tip AC 45 plug or a 46. maybe lower the fuel level alittle below the sight plug.

Holley elec choke does come off quick.

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post #12 of 16 (permalink) Old Jul 14th, 04, 05:05 PM Thread Starter
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Is there a "transfer slot" on the secondary side of a vacuum secondary Holley?
I don't recall seeing one when I opened the plates.
Or is it possible that with the secondary plates opened, it could pull gas from the secondary metering block and give the rich condition?
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post #13 of 16 (permalink) Old Jul 15th, 04, 01:09 AM
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No transfer slots on secondary side of a vacuum sec carb. With sec plates barely open, no fuel is pushed into the air intake.
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post #14 of 16 (permalink) Old Jul 15th, 04, 04:27 AM
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go here adj to these specs:
http://holley.com/HiOctn/TechServ/TechInfo/FMCTech.html


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post #15 of 16 (permalink) Old Jul 15th, 04, 04:31 AM
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HOLLEY tech support:
http://www.holley.com/TechService/Te...iceRequest.htm


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