Idle problem. - Team Camaro Tech
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post #1 of 13 (permalink) Old Jul 9th, 00, 03:47 PM Thread Starter
 
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I have a problem with the idle for my Camaro. I have a V-8 350 small block. The carb is a Holley 750 DP, brand new. The car starts right up and will idle in Park. But when I shift into Drive or Reverse, the car wants to quit. Also wants to quit at low idle when in gear such as stopping the car at a stop sign and such. But after I drive the car for awhile, it is fine at idle in these situations. Have an auto transmission, but to get running I have to hit the gas as soon as the car is put in gear. That doesn't always work either. Adjusted the floats and the idle mixture. Haven't done anything else to the carb. I'm not sure it is the carb, but I would like any opinions. BTW the distributor is a HEI and is also brand new. The vacuum source is on the side of the carb. I set the timing already. The car runs smooth except for what I described above. Any help is greatly appreciated!! Thanks!
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post #2 of 13 (permalink) Old Jul 9th, 00, 05:30 PM
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Are you running a stock cam? A large cam needs a looser convertor or more airflow at idle. It sounds like the same thing mine did. If I adjust the carb mixture screws when the engine is warm, it runs lousy when cold until it warms up (I have no choke). I turned the mixture screws out (counter-clockwise) 1/4 to 1/2 turn beyond the warm idle settings and the cold running is much improved. It does make it a little richer than you need for warm operation. The correct fix is to install a working choke. My carb is a Speed Demon and the chokes are on back-order; when they arrive I will re-adjust the carb.

Jody
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post #3 of 13 (permalink) Old Jul 9th, 00, 05:43 PM
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I too have problems like this, accept my car missfires or detonates (it just like "clicks" and then dies, or almost dies sometimes) when i do start to go. I think it might be my spark plugs though. I'm thinking they are too cold. I took them out and they were covered in black carbon, and they are only about a month old, in the month old engine, and my problem wasnt there the 1st couple days, and it gets worse by the day. I havent driven it in a while because of this. BTW the plugs are NGK R5671A-7s (real cold), i'm going to switch to the 6's, since sometimes the cold plug can't burn off the carbon. Hopefully this will help. Only other thing i can think of is something with the carb-but i dont think it would cause this. Ive tried all different mixture adjustments, timing, and nothing helps. I might need to change the jetting or squirters, but i dont think the stock ones would cause this bad of a problem. Gas mileage sucks right now too.

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post #4 of 13 (permalink) Old Jul 10th, 00, 05:32 AM
 
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TO much carb.
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post #5 of 13 (permalink) Old Jul 10th, 00, 05:56 AM
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What happens when you adjust the idle up a little? I also agree, that may be too much carb for your 350.......KZ
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post #6 of 13 (permalink) Old Jul 10th, 00, 10:01 AM Thread Starter
 
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Hi,
First off, I have a manual choke on the carb. But I can't choke the carb at all or the engine quits. Not even partial choke. Second, the cam is a Comp Cams 268 high energy model. This is definitely bigger than the stock cam. Also, the idle is 750 RPM and the high idle seems to be around 1200. Since I can't choke the carb, are you saying that I should up the 750 idle? I already set the idle mixture a little rich, and the problem persists.
BTW: I am considering changing to an Edelbrock performer 600 cfm carb. But I want the Holley to work. I got the idea for the work I have done to my engine from Chevy High Performance magazine. Late 1999, I think, they did a build up on a GM Goodwrench 350 engine. I changed everything on my engine except for the block, crank, and pistons. Followed their buildup and used the exact parts that they used. They squeezed 400 HP and 430 lb/ft torque out of it. They used the Holley 750 DP and loved it. Had no problems with the size of the Holley in relation to the engine. So I don't think the carb is too big. But they said that a person could decide to use a 600 or 650 cfm carb. Only would sacrifice a little power in return for improved fuel economy and "streetability".
Any ideas are a help. I'll try to increase the idle and see what happens. I'll post back. Thanks.
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post #7 of 13 (permalink) Old Jul 10th, 00, 04:08 PM
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7dragons,
After thinking about it for a minute, I may have an answer for you.
While reading your post, I figured the engine has all the symptoms of too little choke.

Then I read where you tried more choke and the enigne dies.

I think the engine dies because pulling the choke also increases engine speed through the fast idle cam.

What you need is to lower the idle speed on the fast idle cam screw on the right side of the carb, and then the choke blade will be in a more closed position relative to the idle cam when you pull the choke control.

In other words, you need more choke but less fast idle speed.

I don't have a choke like that in front of me to see if there is another way to get more choke blade angle sooner without increasing fast idle as soon. Maybe by adjusting the choke blade itself.

The fact that it runs fairly well by the time it gets warm tells me you can make it run OK if you get the choke right.

What intake do you have and is the heat riser passage open? and do you have headers?

David

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post #8 of 13 (permalink) Old Jul 10th, 00, 04:21 PM Thread Starter
 
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Hi,
I have an Edelbrock Performer RPM manifold. For Idle-5500 RPM, fits the Chevy vortec heads bolt pattern. The heat riser passage is open. I have Hooker Comp headers on the engine. Help any?
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post #9 of 13 (permalink) Old Jul 10th, 00, 04:29 PM
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I'd like to add that with an automatic you should generally run a vaccum secondary carb.

A double pumper would give more throttle response but is more critical to being just the right size, a little too big on a DP carb and you can get a bog.

If running low gears like 4.10 or lower, and a four speed on a 350 with a healthy cam, the 750 should be an ideal size for best performance.

Get the car in high gear and floored at about 5000 rpm and try letting off the throttle just the tinyest bit and see if the car pulls better. If it does, you need a smaller carb.

I had an 800 DP on a LTI 350 with 4.56 gears and headers, ported angle plug iron heads, single plane manifold, etc. I noticed it went better when I backed off in high gear. When I put in a hotter cam, it took all the carb had then. I then swapped in a 750 DP a friend had and noticed a small drop in power and first gear "jump". He had a Z/28 with stock solid lifter cam and 4.10 gears, and headers. He tried my 800 and it was too much for his car. He ran best with the 750 DP.

Based on this experience, I bet there are a lot of factory stock Z/28's with 780's that never have their secondaries open fully! I'd like to rig up an indicator light on a 302 Z/28 carb and see if I'm right.

The 780 has the same venturi size as the 800 I had. and if it was too big for my 350 It probably would have been too big for a 302.
David

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post #10 of 13 (permalink) Old Jul 10th, 00, 04:32 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by 7dragons:
Hi,
I have an Edelbrock Performer RPM manifold. For Idle-5500 RPM, fits the Chevy vortec heads bolt pattern. The heat riser passage is open. I have Hooker Comp headers on the engine. Help any?
<HR></BLOCKQUOTE>

Yeah,
The headers will prevent quick warm up because you don't have a heat riser valve to force the hot air thru the manifold.
The fuel is just laying there probably drooling into a couple of cylinders more than others.

Try the choke adjustment I suggested and let me know how it goes...
Good luck, David

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post #11 of 13 (permalink) Old Jul 13th, 00, 02:57 PM Thread Starter
 
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Hi,
I adjusted the fast idle and it seems to have done the trick. Now the car starts in gear just fine. No more embarrassment when the darn thing would quit while trying to pull out of the parking lot at Wal-mart! Thanks alot!!
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post #12 of 13 (permalink) Old Jul 14th, 00, 01:45 AM
 
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Hey 7 what tipe of exhaust are you using once i had a 750 on my mild sb open headers perfect plug it with to small tubing crap maybe to restrected?
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post #13 of 13 (permalink) Old Jul 14th, 00, 11:20 AM Thread Starter
 
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I have 1 5/8" Hooker Comp headers running to Flowmaster dual exhausts. It's running fine now. Knock on wood!
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