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Old 10-27-2005, 06:58 PM
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no idle ajustment

I recently purchased a 74 corvette with a L82 drivetrain that's been sitting. The engines had one typical rebuild,(+30, 10:1,) The only unusual change was the addition of a GM 327/350HP cam 222dur/460lift. The carb and distributer were fubared so I bought a new HEI distributor with a HP advance curve kit, and a holly 600CFM carb -electric choke, vac. secondaries . Once the timing was set the car starts great, the choke activates, and releases properly. The only odd thing I noticed was that I had to run the base idle screw all the way out to get the idle down to 650rpm. For the first 10-20 minutes of driving the car idles great , even has a little lope but then as the car gets hot, the idle picks up all by itself to a consistant 875rpm and theres no idle adjustement left. Its not the accel. cable, I took it off and it still stays up. The choke appears to be full off. I adjusted the idle mixture for max vaccuum and if anything that speeded it up a little. Also , if anything the timing could stand to be advanced a little more, but that would only speed it up more. Could I have some sort of vaccuum leak? or any other suggestions??

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Old 10-27-2005, 08:10 PM
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hi ,

you cant keep your engine running with the idle screw all the way up , the engine vacuum needs at least .02" butterfly open . You should se a square from the idle grove in the venturis beneath the barrel, one turn in well do!!

then adjust the idle mixture screws , maximum vacuum is not always accurate coz it could be maintained even with a 3\4 turns over .

It should be 1 to 1 1\2 turns out for stuck 350. Changes must be done at the operating temperature.

And check for a week spring.
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Old 10-28-2005, 06:21 AM
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Doc here,

FIRST: Welcome to the Board

Check to be sure the IAC (I think that's what they call it) Solenoid for the A/C is backed all the way down, (provided it's still in place) This will hold off the Throttle linkage...

When it's idling fast , look to see the throttle is all the way against the stop...and not held off a bit..If it is, put a little pressure on it and see if it slows up..If it does something in the linkage train is binding...

Check your choke linkage...If the linkage is over bent, or over adjusted it can hold the throttle open just a bit..

On the Jets...

On a warm engine, Choke fully open, Idle at 750 MT or 950 AT (or as close as you can possibly get..)

Turn either jet in carefully until the engine sputters and dies..

back it out 3 turns..restart and do the same with the other jet...

Be careful not to over-tighten and bottom them out as they are brass and will score and become useless if you do this...If they don't respond, It's time for rejet/rebuild..

Now one at a time..slowly adjust each for highest idle..

Then going forth and back, making small adjustments, and allow 5 to 10 seconds for the engine to normalize (burn off excess fuel) tune for highest idle, with no random pop or stumble..

Take your time in so doing..or you'll tune right through the "sweet spot"...and when your satisfied, go to the rear and should NOT smell any raw fuel..(or anything for that matter)

If you feel you may have a vacuum leak , use your gauge..should be 17 to 20 in Hg..(unless you have a REAL lumpy cam) Lower might indicate a leak..Spray Carb cleaner around the manifold and carb (with air cleaner on..over-spray will false trigger) anywhere it speeds up you have a leak..

If your headlight doors and wiper well doors are vacuum..put them BOTH in bypass as these will leak and effect engine performance and ALSO drive you nuts trying to find them on the engine...If you have to, plug the canister in the nose piece..

That should get you started..


Last edited by docvette; 10-28-2005 at 06:23 AM. Reason: Bumbling Bigthumbitis
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Old 10-28-2005, 06:41 AM
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Idle RPM increases with engine temp.

If after checking everything else that's been mentioned already you may be too lean on your idle adjustments. If the RPM increases with temp, it's normally an indication that you're too lean.
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Old 10-28-2005, 08:54 AM
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Check the carb's secondary's. They may be a little to far open. The previous owners may have jacked around with the secondary's trying to get the car to run since the dizzy was messed up.
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