454 running hot at idle - carb tuning problem? - Team Camaro Tech
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post #1 of 4 (permalink) Old Jan 22nd, 07, 03:24 PM Thread Starter
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454 running hot at idle - carb tuning problem?

Hi all, my 454 is running hot at idle (I shut it down yesterday once it hit 200). Off idle, the temp drops down to about 190. The Edelbrock folks (Edelbrock perf. 750 cfm carb. electric choke) told me that more than likely it is running too lean and that I should set idle A/F mixture to get the highest consistent vaccuum - which sould fix it.

Here is my question (I searched a lot of posts before writing this, but many were maybe too advanced for me/my application):
Can anyone tell me/or direct me to somewhere that talks in detail about how to set the idle mixture? Perhaps it is just too simple and no one really needs it to be explained to them.
I have hooked up a vaccuum gauge to the ported vaccuum port. Now I am supposed to adjust one of the two idle screws until I get the highest constant vaccuum, right? I think counterclockwise is leaner and clockwise is richer (but could be backwards). How much do you have to turn the screw? Seems like when I do it, the vaccuum reading will go up, and then down, and then fluctuate.....idle speed will likewise go up and down. Is there any easy way to know when you are at the right spot with the first screw? Is it okay to first go completely lean or rich and then bring it back slowly the other way?

Then you adjust the second screw. What am I looking for when I do that? Do I want my idle speed to increase decrease or stay the same? How about the vacuum?

The manual that came with the carb gives some directions on how to do this, but they seem geared to someone with a little more experience than me. For instance they say go lean a little, but I am not certain what a little means.

I know I can bring it in to have it tuned, but I have done everything up to this point and would like to have a stab at it first.

Again, I know this may be a stupid question that everyone knows the answer to.

As always, thanks,
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post #2 of 4 (permalink) Old Jan 22nd, 07, 03:43 PM
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Re: 454 running hot at idle - carb tuning problem?

the problem might not even be the carb...rich or lean, you shouldnt overheat at idle....actually sounds like not enough timing at idle...anyway, turn the idle screwsout to the highest idle, and then turn them back in until the idle just drops off...then back out a quarter turn...you are doing this all within about 3 full turns of the screw...when you are turning the screw in, you are leaning the carb out...you want the car to run as lean as possible at idle without creating a lean condition off idle, and thats why you turn it back out a quarter turn
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post #3 of 4 (permalink) Old Jan 22nd, 07, 04:18 PM
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Re: 454 running hot at idle - carb tuning problem?

First, I see one glaring error in your post, hopefully just a typo. You do NOT want the gauge on the "PORTED" vac port, you want it on the "full" port. On an ede, it's the one on the drivers side of the carb, and with a stock type cam it should should about 18 at idle, less, perhaps much less, if you have a bit of a "cam" in it.

I agree with the post above. You should check your timing. Pull the vacaum hose off the distributor and stick a pencil in the end. Hook up your timing light to #1 plug wire (front, drivers side) and connect the black clip to a good ground, and the red clip to battery power, pull the trigger and aim it at the timing tab on the front, drivers side of the timing cover. You'll see the line on the balancer "freeze" when the light flashes.

Dial in about 12-14 degrees of timing, that will be near the end or a lil off the end of the tab. you do it by loosening the clamp at the bottom of the distributor and rotating the distributor by pulling the vac advance can toward you. The idle speed will increase when you do this.

Turn the idle stop screw counter clockwise to bring the idle back down to where you like it. 800 rpm or so on a mild motor.

Take the pencil out of the vacaum hose, attach the "tee" that came with your vac gauge, and connect both the guage and the vac advance with some spare hose.

Check where the distributors hose is plugged into the carb. We want it on the drivers side port. If it's on the pass side, move it, and plug the empty one.

The idle speed will increase, crank it back down.

Shut the motor off, and ballpark your mixture screws. Turn them clockwise till they just lightly bottom, counting exactly how far, then preset both at 1 1/2 turns out from bottomed.

Note, clockwise is lean, counterclockwise is rich.

Fire it up, and check your idle rpm and vac gauge reading.

Adjust the mixture screws for highest vacaum. These are VERY sensitive, 1/8 turn at a time, always both exactly the same, zap the throttle then let the engine stabilize after every turn, then check the guage. The 1 1/2 turns will probably be a lil rich, so start by cranking them in. If the idle speed increases, crank it back down.

Finally, if it's an automatic, have someone sit in the car, stand on the brake, and put it in gear, and recheck the vac and idle speed.

The specifics here are geared toward a stock or near stock motor. If yours is more radical, give us some details, we can do better.

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post #4 of 4 (permalink) Old Jan 22nd, 07, 08:00 PM Thread Starter
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Re: 454 running hot at idle - carb tuning problem?

Hi Guys, thanks so much for your help. I am going to follow these to the letter and see how I make out. It is a stock motor, so I think it should work out fine. I will start with the timing and then move onto the idle. Thanks again, this is going to be a great help!
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