Poor Idle, Rpm bounces and won't run - Team Camaro Tech
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post #1 of 16 (permalink) Old Apr 18th, 11, 07:25 PM Thread Starter
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Ken
 
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Poor Idle, Rpm bounces and won't run

My 350 has only a few miles on it since the rebuild, but was running well until 1-2 weeks ago. The rpm's bounce about 500 rpms and I have to keep gas on it or it will die. It has no power and the exhaust smells bad. I checked the plugs and they are black. I am concerned because one on the plugs on the pass side was loose. I cleaned the plug and tightened it, but i can't get it to idle properly. Can a loose plug cause a burned valve on a motor that has not really been driven?

Last edited by CamFrk68; Apr 18th, 11 at 07:47 PM.
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post #2 of 16 (permalink) Old Apr 18th, 11, 08:15 PM
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Wes
 
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Re: Poor Idle, Rpm bounces and won't run

A loose plug won't cause any harm.

Give us more details;

What carb?
What distributor and ignition?
What is your timing set at and how was it set?
What heads and which spark plugs (maybe too cold?)?
What do you mean by no power? No RPM? No seat of the pants? Does she miss?
Any other symptoms?

Any other details about the engine would help.
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post #3 of 16 (permalink) Old Apr 18th, 11, 08:55 PM Thread Starter
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Ken
 
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Re: Poor Idle, Rpm bounces and won't run

I am running a Carter AFB 625. (the carb does not have a choke and is missing the butterfly over the primaries) I have not had an issue.
I am running an Gm HEI distributer and have 6 degrees of timing. Timing was set with my timing light and i did unplug the advance when I set it.
I have Edelbrock RPM heads and have a champion plug that is recommended for the head.
When she idles the rpms go up and down about 500 rpms, When the rpms fall the motor dies. If i put it in gear it dies unless i bring rpms up to about 1500 rpms. The car struggles to move without dieing.
At first I thought I had a vacuum leak because of the RPMs going up and down but can't seem to find a leak.
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post #4 of 16 (permalink) Old Apr 18th, 11, 08:57 PM Thread Starter
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Ken
 
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Re: Poor Idle, Rpm bounces and won't run

I am running the voodoo 268 cam, 9.73:1 compression. The motor was built last summer and may have 5-10 actual miles on it.
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post #5 of 16 (permalink) Old Apr 18th, 11, 09:14 PM
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Bill
 
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Re: Poor Idle, Rpm bounces and won't run

Had the same problem 2 weeks ago. New engine, maybe 200 miles
on it. I took it to the guy who built the motor and he re-jetted the
the carb and checked timing, vacume leaks etc. It ran better but
idled at 700 then dropped to 500 then tried to die out. He did pull
a plug and found it to be fuel fouled. I went and got some new ngk
plugs and gapped them at .035 instead of the old gap of .055. After
putting in new plugs car ran and idled perfectly. Maybe all I needed
was to change plugs.
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post #6 of 16 (permalink) Old Apr 19th, 11, 04:19 AM
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Re: Poor Idle, Rpm bounces and won't run

I too had the same problem about 2-3 weeks ago. I turned the mixture screws counter clock wise 1/4 turn each and It got alot better.
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post #7 of 16 (permalink) Old Apr 19th, 11, 11:01 AM
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Wes
 
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Re: Poor Idle, Rpm bounces and won't run

A couple of thoughts:

1) Are the weights and springs that activate the mechanical advance sticking causing inconsistent idle? Wouldn't hurt to apply a small amt of grease on the contact areas of the weights.

2) Could the throttle blades in the carb be sticking, causing to them to correctly close sometimes and not others. When it's idling too high, can you manually (by hand) close the throttle blades further by working the linkage and reduce the idle?

2a) What about the linkage? Any binding?

3) It could be that sometimes she's correctly idling on the idle circuit, and other times idling on the transition circuit. Does she ever diesel (run-on after ignition is turned off)?
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post #8 of 16 (permalink) Old Apr 19th, 11, 11:12 AM
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Alan
 
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Re: Poor Idle, Rpm bounces and won't run

Well, he does state the plugs are fouled and the exhaust smells really bad>Running rich? Pull the plugs, clean them, check the gap. Then I would look at the carb. Trash in the needle and seat?

alan
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post #9 of 16 (permalink) Old Apr 19th, 11, 11:18 AM
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Re: Poor Idle, Rpm bounces and won't run

Your Voodoo 268 cam has 227/233 @ .050" duration. That cam in a 350 will idle fairly rough. I would increase the initial timing to 10 degrees and adjust the idle mixture screws with a vacuum gauge. You also might want to replace the plugs before doing this.

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post #10 of 16 (permalink) Old Apr 20th, 11, 10:27 PM
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Re: Poor Idle, Rpm bounces and won't run

i agree on dripping fuel on ventures(needle seat)--remove bowls and clean-chek power valve and let it run as often as you can
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post #11 of 16 (permalink) Old Apr 21st, 11, 07:30 AM
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Al
 
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Re: Poor Idle, Rpm bounces and won't run

Before you mess with the carb, get the timing set. 6 BTDC initial @ idle means nothing - you need to set the total timing. Disconnect and plug the VA, then set the timing at 36 BTDC @ approx 3500 RPM. Let it idle back down and see where your initial timing is, and use that for future reference. Once you get that done you can start tuning the idle speed and mixture.


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post #12 of 16 (permalink) Old Apr 21st, 11, 07:46 AM
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Re: Poor Idle, Rpm bounces and won't run

Quote:
Originally Posted by bpos View Post
before you mess with the carb, get the timing set. 6 btdc initial @ idle means nothing - you need to set the total timing. Disconnect and plug the va, then set the timing at 36 btdc @ approx 3500 rpm. Let it idle back down and see where your initial timing is, and use that for future reference. Once you get that done you can start tuning the idle speed and mixture.
x2
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post #13 of 16 (permalink) Old Apr 21st, 11, 08:59 PM
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Re: Poor Idle, Rpm bounces and won't run

i disagree on timing 36 is for racing -sounds like this is street motor and daily driver which i would put 32 total-the problem in this issue is probably carb but timing should be chek first if there is no fuel dripping in ventures
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post #14 of 16 (permalink) Old Apr 21st, 11, 09:05 PM
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Re: Poor Idle, Rpm bounces and won't run

I'll go along with the total timing being most important. I run a 383 stroker with a pretty wild cam, 770 Street Avenger.....had real issues getting a reasonable idle. I have 38 degrees total and 17 initial, then set the idle screws with a vacuum gauge, looking for the highest vacuum reading.
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post #15 of 16 (permalink) Old Apr 22nd, 11, 09:14 PM
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Re: Poor Idle, Rpm bounces and won't run

right on bill--got any numbers at track --i loved my 383-kinda miss those smallblocks
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