RPMs wont go down after hitting the throttle at idle - Team Camaro Tech
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post #1 of 13 (permalink) Old Mar 27th, 10, 01:52 PM Thread Starter
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RPMs wont go down after hitting the throttle at idle

New 350 290 hp crate motor, new fuel pump, new HEI, used Edelbrock carb. It started right up, idled nice, set the timing at 10 degrees, set thye idle but when I blipped the throttle, it went up to 1800 rpms. It keeps doing this and I cant figure it out. Put on new vacuum lines. Checked for vacuum leaks, checked for correct carb gasket, checked for throttle linkage binds, checked auto choke wires, etc. Any thoughts? The carb worked fine when I took out the engine.
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post #2 of 13 (permalink) Old Mar 27th, 10, 02:25 PM
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Re: rpms wont go down after hitting the throttle at idle

Check the timing advance with a timing light. Sounds like the mechanical advance may be kicking in too soon and once you reach that point, the RPMS increase. Do you have vacuum advance on this engine?

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post #3 of 13 (permalink) Old Mar 27th, 10, 02:39 PM
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Re: rpms wont go down after hitting the throttle at idle

linkage is hanging either at the carb or in the floor or where the linkage comes thru the floor to the carb.

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post #4 of 13 (permalink) Old Mar 27th, 10, 03:17 PM Thread Starter
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Re: rpms wont go down after hitting the throttle at idle

the rpms go up whether I hit the pedal or take the pedal linkage off and hit the carb throttle. The distributor (new) has a vacuum canister but ive put the line in both ports (one full vacuum and one ported), with no difference. Not sure its a vacuum problem as a sprayed carb cleaner everywhere with no change in rpms. If I push down hard on the carb throttle the rpms slow down but as soon as a blip it, up again.

Last edited by wheezer; Mar 27th, 10 at 03:36 PM.
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post #5 of 13 (permalink) Old Mar 27th, 10, 03:54 PM
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Re: rpms wont go down after hitting the throttle at idle

Try another carb as the throttle plates are rubbing against the bore.

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post #6 of 13 (permalink) Old Mar 27th, 10, 04:20 PM
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Re: rpms wont go down after hitting the throttle at idle

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Originally Posted by Everett#2390 View Post
Try another carb as the throttle plates are rubbing against the bore.
X2 Internal vacuum leak causing the idle to fluctuate. Also check for any unplugged or cracked vacuum lines or intake leak.

I NEED TO HIT THE LOTTERY
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post #7 of 13 (permalink) Old Mar 27th, 10, 05:32 PM
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Re: rpms wont go down after hitting the throttle at idle

alright, have you checked your air bleeds?

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post #8 of 13 (permalink) Old Mar 27th, 10, 07:38 PM
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Re: RPMs wont go down after hitting the throttle at idle

Secondaiys mis ajusted or mislalgned, or to much play/wear in the butterfly bushs

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post #9 of 13 (permalink) Old Mar 28th, 10, 09:08 AM
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Re: RPMs wont go down after hitting the throttle at idle

Here's another thought. Carberators have choke mechanisms on them. When the engine is cold, the choke plate closes to make the motor run rich. In addition, a little stepped cam under the choke housing is suppose to raise the idle speed. It's called the fast idle cam. It's weighted so it will fall down away from the fast idle stop screw. When the engine is cold, the choke spring pulls it up and essentially engages another idle stop setting - the fast idle setting.

If the choke is not properly set up, you could be having problems with the fast idle cam. Also, on my Holley, I had problems initally with linkages binding up and preventing the fast idle cam from dropping away from the fast idle stop. Usually you can diagnose this quickly by partially cracking the throttle by hand to lift the primary throttle shaft off the fast idle stop. Then manually open the choke plates wide open. This *should* force the fast idle cam to drop. Let go of the throttle shaft so that it sets on the curb idle screw - it should idle normally then. Of course if the choke linkages aren't correct, or some other alignment problem exists, this last quick test may not work.

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post #10 of 13 (permalink) Old Mar 28th, 10, 12:07 PM
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Re: RPMs wont go down after hitting the throttle at idle

I keep forgetting about the choke...most of the classics here we remove the chokes as we dont have the cold temps most of you guys have.

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post #11 of 13 (permalink) Old Mar 29th, 10, 05:01 AM Thread Starter
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Re: RPMs wont go down after hitting the throttle at idle

Thanks. Dont know what is wrong with the carb but it was the carb (got another carb and it ran fine).
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post #12 of 13 (permalink) Old Mar 29th, 10, 07:09 AM
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Re: RPMs wont go down after hitting the throttle at idle

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Originally Posted by wheezer View Post
Thanks. Don't know what is wrong with the carb but it was the carb (got another carb and it ran fine).
Nice job and thanks for the update.. Ive had a carb giving me the same problem "internal vacuum leak" don't know from what maybe just old ware and tare.

I NEED TO HIT THE LOTTERY
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post #13 of 13 (permalink) Old Mar 30th, 10, 11:21 AM
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Re: RPMs wont go down after hitting the throttle at idle

And maybe the old carb is savable. Check the return spring on the throttle shaft. It might be weak, missing or placed in the lightest tension hole of its linkage. My new Retrotek FI was doing the same thing as yours. Cory, at the factory, said to put a second return spring on the secondary shaft. That wasn't it. The primary shaft return spring was in the lightest hole. Moved it up one notch, end of problem. And the throttle arm return spring is good. It should be! It's original. And that reminds me, forgot to tell Cory. Gotta call.

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