High RPM upon startup - Chevelle Tech
Troubleshooting Diagnosing problems done here.

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post #1 of 4 (permalink) Old Jun 2nd, 08, 4:42 PM Thread Starter
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Join Date: Jun 2003
Location: Chula Vista, CA
Posts: 113
High RPM upon startup

Hope someone can give me some advice on a High Idle problem.
History: My Chevelle has a 355, MSD 6 HEI, and now, a Edelbrock Performer Dual Quad manifold and carb kit. The car was running perfect beore, but I decided to take it a step further by adding dual quads instead of the singel carb setup I had before.
I know, if it aint broke, don't fix it. Someday I'll do just that.

When I start the car now, it quickly jumps to about 3200 RPM. I kick the accelerator pedal, but it just increases the RPM and settles at 3200 again.
I don't keep it running more than a few seconds because of fear of damaging the engune.
I have cked the vacuum ports for leaks, and throttle linkage for binding, fuel pressure, etc, all were fine.
The only thing I have not been able to ck is the electronic choke for good voltage. Could a nonenergized choke cause this problem?
I have not adjusted or changed any of the factory settings of the carbs or choke.

If someone could give me some basic things to ck, I'd appreciate it. I changed the timing by a hair to see if it changed the symptoms, it had no effect.

Thanks all!


72 Chevelle SS, (clone)355, 350 auto, Pics at http://community.webshots.com/user/phipwood
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post #2 of 4 (permalink) Old Jun 2nd, 08, 6:39 PM
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Location: Lakewood, WA
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Re: High RPM upon startup

If the choke flap is closed without energy, this will cause the fast idle. Or at least part of it.
With the engine off...look down the carb with the choke. Is the primary butterfly open? Is the linkage binding? Got some good (2) return springs? Fighting 2x the resistance now...
Gasket causing something to stick?

George Kettler
o SOLD 8/2016 my beloved 1970 Elky 496.
o 68 Vette 427/M-20/3.36 23 year owner
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post #3 of 4 (permalink) Old Jun 2nd, 08, 9:04 PM
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Mr Bill
Join Date: Aug 1998
Location: Waldorf Md. USA
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Re: High RPM upon startup

If the throttles are closing all the way, then it really sounds like a vacuum leak to me. Also amke sure the chokes are open all the way, hold them open with some wire if you have to. Double check everything, I have been fooled in the past and missed a vacuum port. If the car has power brakes, take the line off and plug it, the booster might be bad even though it would be pretty rare for it to fail just like that. Which manifold number do you have and what carbs ? Is the manifold designed for use with spread bore carbs like the Q-jet ? If so and you are using Holley's or Edelbrocks you might need the thin plate they make to go under the carb. Post the manifold part number and the carbs you are using and I will look in the catalog.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md


1971 Heavy Chevy - original owner
1984 Buick Riviera - original owner (Wife's car)
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post #4 of 4 (permalink) Old Jun 3rd, 08, 1:53 AM Thread Starter
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Join Date: Jun 2003
Location: Chula Vista, CA
Posts: 113
Thumbs up Re: High RPM upon startup

Thanks all who replied. I did some more troubleshooting and found I had a misadjusted fast idle screw and the linkage to the second carb was incorrectly adjusted, it wasn't allowing the throttle to fully return.

Thanks again, things are much better now, all I have to do is timing and a little more with idle.

72 Chevelle SS, (clone)355, 350 auto, Pics at http://community.webshots.com/user/phipwood
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