I posted this in performance already and then thought maybe it belonged here in the first place (Sorry about that).

I'm having a problem with my edelbrock 600 carb. I just put it on and I cant seem to get it to idle under 800 rpm. The trottle cable isnt hanging up, the spring is tight so it's pulling the trottle back. The only thing I didnt check is maybe it is hanging up somehow on the adaptor plate. The idle adj. screw can be backed all the way out and it still will not idle under 800 rpm. Everything runs good except for this high idle. The factory idle is suppose to be 700 rpm. Anything over that makes it jolt when you put it in gear. This is on my Chevy truck not my chevelle but I still could use some advice. Thanks

This is a responce that I posted to someone that mentioned a vacuum leak in the performance forum.

Scoots,
Sounds like a possiblity, but let me say that this is a very smooth running motor with a very steady vacuum reading (at present idle mixture and curb idle it has about 20" of vacuum). It dosent miss and it dont seem to be running rich. So, with that said do you think a vacuum leak is still possible? Thanks for the idea please keep them coming.
Sorry again for the improper posting.


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66 chevelle thats in the middle of restification. 454 th350 12 bolt posi, global west rears, and more goodies in the rafters waiting to go on
Member #387

[This message has been edited by pop (edited 10-29-2002).]

The mechanical idle screw on the drivers side assembly bumps the primary plates open to achieve enough air for idle. Either the plates are NOT shutting all the way due to faulty mechanism (has yours been taken apoart?)or they are hanging up on the intake from below...or....there is another way there is air getting thru or around the carb. These are the only two scenerios that allow air thru!

What type of intake are you using. Are you using a spread bore type. If so, and I have seen this, you need an adapter plate to allow the square AFB base to fit and seal properly.

I am assuming that you have made sure that the choke is COMPLETELY off...or that will keep the idle up slightly.

I assume you have a manual, but if not.... check out http://www.edelbrock.com/automotive/index.html for more information.

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Steve Jack
-Concept One Pulleys and Brackets
-Marketing Technologies Limited
-Northern/Southern Rodder Magazine's "Jack'Stands" technical column author/originator

Steve,
Ya, I do have the adaptor plate for a spread bore to a square bore, and it's the one with the 4 holes in it. No, it's almost a brand new carb, I bought it for the chevelle before I got the 454.
The choke is working fine totaly disengages once it warms up. I think that your probably right, I either have a vacuum leak around the carb for some reason or the blades arent closing all the way. Let me add that I can stall the engine with the idle screws pretty easy when it's at idle. Let me ask this, do you think that you should be able to stall the engine or at least get it to idle bad by turning the idle screw out all the way? If not maybe the clunck is do to a bad motor mount or trans mount (this is a 4X4), the u-joints check out fine. The jolt is mostly when it's put into reverse. Like I said this thing runs smooth and it dont really seem like the Idle is way out(I used a tach/dwell meter and a vacuum gage to tune), but I do get the hard shift into reverse and I cant bog the engine down with the idle screw. If the idle screw itsnt suppose to be able to bog it down, then I wonder if someone else has had a 3/4 ton Chevy 350/th400/np208/14 bolt semi floater that has had a similar problem. Let me know what you think. Thanks, Nick

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66 chevelle thats in the middle of restification. 454 th350 12 bolt posi, global west rears, and more goodies in the rafters waiting to go on
Member #387

[This message has been edited by pop (edited 10-29-2002).]

Well ,
I checked the mounts and they are tight. I started looking around the carb and in it with a flashlight everything looked good and from what I could see the throttle plates at least look like there closing well from the top. Both gaskets between the carb, adaptor, and the manifold look to be in there proper position. On futher inspection I found the front intake gasket on the intake manifold was pushed out and also cracked in two from what it looks like. I tried the propane trick at the crack where it was pushed out to see if the idle would go up but it wouldnt. So, do you guys think that this is the culprit. Thanks

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66 chevelle thats in the middle of restification. 454 th350 12 bolt posi, global west rears, and more goodies in the rafters waiting to go on
Member #387

Pop,....First...the mixture screws on the front...how far out are they? You need in the neighborhood of 1.5 to 2 turns out on both. If not, it's probably too lean...come out at least 1.25 turns equally on both! The adapter plate thing can be a problem from the bottom as well as sealing. My experience is that the plate can hang the plates up and/or poor sealing even though this is what it's designed for.

The mechanical idle screw should be able to be backed down to eventually stall the engine by closing the plates completely (remember the carbs that had the "curb idle and the "stop" idle solenoids...these basically let the throttle stop go all the way back to the fully closed position to shut the air off). If not, it's still getting fuel and AIR.

Sometimes a poor or wrong PVC can cause a problem with idle. Block all the vacuum port off completely...brakes, PVC, distributor advance....everything. This way it can start with anew without the branching vacuum circuits hooked up. Next, using your propane torch (your idea....not mine....since you have it) and go around the base of the carb. If that does not reveal any increase in idle, next take a piece of cardboard big enough to go over the carb. Then while the engine is running try to snuff out the engine. Make sure the cardboard is sufficient enough to not collapse. If you can snuff it out, then it's likely the plates are open ever so slightly, and if you can't....well there is air AND fuel coming in from somewhere?


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Steve Jack
-Concept One Pulleys and Brackets
-Marketing Technologies Limited
-Northern/Southern Rodder Magazine's "Jack'Stands" technical column author/originator

you could have a leaking intake gasket..... but i have a 600 edelbrock on my chevelle and it was alittle tricky getting it set but i think i got.... i had trouble wiht the back butterfly opening up a little and i bent the arm alittle to keep it from moving

Scott

Just a fyi,
I just wanted to say thanks to all that actually tried to help. I ended up replacing the intake with a edlebrock. When I pulled the old stock manifold ( 91,000 original) you could see that both the front and rear end seals where trashed ( used rtv to reseal) . Anyway, truck idles down nice now , and runs a lot stronger. Thanks

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66 chevelle thats in the middle of restification. 454 th350 12 bolt posi, global west rears, and more goodies in the rafters waiting to go on
Member #387