Idling too fast - Team Camaro Tech
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post #1 of 13 (permalink) Old Feb 20th, 10, 09:59 PM Thread Starter
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Devon R
 
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Idling too fast

Hi. I have a 305 with higher compression (smaller than normal cc) heads, a mild RV cam, flattop pistons, headers, and a Performer carb and intake.
I had a flooding problem with a few Holley carbs(Which I had posted about in a previous thread), so I dropped a brand new 1406 Edelbrock Performer carb on it.

It started right up! Problem is, now it won't slow down.

The engine idles at 3,000 RPM, and it doesn't matter if the engine is warmed up or not. I've even held the choke plate open with a screwdriver, and no change. So, the electric choke should not be affecting it any, right?

The (lean/rich air/fuel mixture) screws don't have any effect. The idle speed screw on the linkage doesn't have any effect. The hi-speed screw under the linkage doesn't have any effect.

We've checked, and can't find any air/vacuum leaks. New hoses, etc.. What all could cause this? Just fuel or air, right?

Could the intake manifold be leaking INTERNALLY to the engine, and sucking in air that way? Could the brake booster be leaking vacuum and cause this? I've sprayed WD-40 around the engine, carb, intake, etc, while it was running, to try and find a vacuum leak: nothing.

3,000 RPM is WAYYYY too high for a simple air leak, isn't it? This is a non-computer engine, with vacuum advance HEI distributor, so it isn't a computer or sensor issue.

HELP??? Thanks!
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post #2 of 13 (permalink) Old Feb 21st, 10, 11:01 AM
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John
 
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Re: Idling too fast

Since you seem to have ruled out the probability of vacuum leaks, let me confirm..... Did you use the correct NEW gasket? I ask because the last Edelbrock I used came with some cheesy base gaskets that leaked. I bought Felpro and all was good.

If there is no response to any of the adjustments to the primary throttle, check the secondaries. Make sure that the secondaries are COMPLETELY CLOSED at idle. Make sure they are not hung up on a gasket or such. Confirm that the linkage is allowing them to close. adjust if necessary.

You say that you held the choke open?? Is the choke opening all the way when warm? If it is not, it must be adjusted accordingly. The electric choke should be open within about 3-5 min with 12volts applied.

Have you looked for the simple stuff like gas pedal linkage hung up, or shift cable not adjusted holding the throttle plate open?

You may have to check all the baseline adjustments again according to Edelbrock specs......Jb

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post #3 of 13 (permalink) Old Feb 21st, 10, 11:08 AM
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Re: Idling too fast

brake booster good?
try plugging the line to the booster.


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post #4 of 13 (permalink) Old Feb 21st, 10, 11:59 AM Thread Starter
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Devon R
 
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Re: Idling too fast

I'll check the brake booster with a vacuum pump/gauge. I'll do the same for the vacuum advance canister for the distributor, just in case. I'll also try putting my hand over the carb to check for vacuum leaks (if it keeps running, it's got a leak). Then I'll post results.

Johnny B: yes, it's a new Edel. I did use their gasket, but spraying WD-40 around the base of the carb while running didn't change things, so I don't think it is leaking? I'll check the secondaries to make sure they are fully closed.

Yes, I held the choke open with a screwdriver: no change. I don't really know if the choke is opening fully when warm because I haven't let it run that long (at 2,500 to 3,000 idle speed, I'm a little nervous to let it run very long!). I've set the choke according to directions, and it doesn't change to open it up manually, so I don't think it is the choke?

Is it possible for an intake manifold to have a vacuum leak INTERNALLY to the engine? How would I check? THANKS, guys!
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post #5 of 13 (permalink) Old Feb 21st, 10, 01:00 PM
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Re: Idling too fast

Besides a vacuum leak of some sort. Make sure the fast idle cam behind the choke assembly is moving freely. You'll have to open the throttle enough by hand to get the fast idle screw to let go. But once you do that, the fast idle cam (really a weighted lever with various idle stops on it) should freely move up and down. My holley 650 CFM electric choke was bound up. I had to bend a couple of rods slightly to get the fast idle cam flopping properly.

Dave
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68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #6 of 13 (permalink) Old Feb 21st, 10, 01:04 PM Thread Starter
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Devon R
 
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Re: Idling too fast

OK, let's see. I found a vacuum leak by using a Mightyvac: the little tubes that run the heater doors, etc, leak down immediately when vacuum is applied. We removed the hoses from the carb, and plugged the port. Idle speed dropped, but only to 2,000 rpm. Shouldn't cold idle be only 1200?

Brake booster and vacuum advance canister on the distributor hold vacuum fine, by the way.

PUt a gloved hand over the secondaries while running; no change. Added a second hand over the primaries: stumbled and started to die, so I removed hands. That doesn't seem to indicate a large air leak present, although it only takes a little bit of vacuum leak to cause a problem, I know.

Shot some carb cleaner around the carb base again: no change in tone or speed.

Secondaries are fully closed with engine off. Do I need to check this with the engine running, too?

Any other ideas?
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post #7 of 13 (permalink) Old Feb 21st, 10, 01:19 PM Thread Starter
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Devon R
 
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Re: Idling too fast

Dave:
We checked, and the fast idle cam is moving freely. The fast idle screw is screwed back so far it isn't even touching the cam, and it still won't set down in speed.

We had this fast idle problem with a Holley we had on the car, too, so I don't think the problem is the carb. Just my gut instinct, combined with the sleuthing we've been doing. (The Holley flooded after we rebuilt it, so we just bought the Edelbrock to eliminate the flooding issue.)

The engine was originally in a different car, with a QJet on it. It seemed to run fine, although maybe a little higher revs at idle than we'd like. That car was totalled by hail after 20 miles on the engine rebuild, so we pulled the engine and put it in the Camaro, with a different (non-computer) carb. Ever since the engine was put in this car, it has behaved this way.

Okay, folks, what do I check or do next?
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post #8 of 13 (permalink) Old Feb 21st, 10, 01:59 PM
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Re: Idling too fast

Adjusted the curb idle screw?
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post #9 of 13 (permalink) Old Feb 21st, 10, 02:52 PM
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Re: Idling too fast

if its an automatic check the modulator for vacum leak.


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post #10 of 13 (permalink) Old Feb 21st, 10, 04:33 PM Thread Starter
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Devon R
 
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Re: Idling too fast

IT LIVES!!
After finding the last little vacuum leak, it set down enough we could adjust the curb idle and the curb idle screw actually DID something! Idles at 750 with that mean little burble, and smooths out as you apply the gas!

Thank you all so much for your help!!!
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post #11 of 13 (permalink) Old Feb 21st, 10, 08:26 PM
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Re: Idling too fast

Sounds like you're making progress but here is something else to check. Make sure the mechanical advance isn't coming in too soon. When your idle speed gets high enough to cause advance it can really mess with you .

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #12 of 13 (permalink) Old Feb 22nd, 10, 03:42 AM
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Re: Idling too fast

Quote:
Originally Posted by 873rdgen View Post
After finding the last little vacuum leak, it set down enough we could adjust the curb idle
Good job!
Vacuum leak was where?

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post #13 of 13 (permalink) Old Feb 23rd, 10, 03:47 PM
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Re: Idling too fast

A propane torch is a great tool for vacuum leak tests - unlit of course.
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