Engine run-on - Team Camaro Tech
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post #1 of 15 (permalink) Old Mar 17th, 11, 04:55 PM Thread Starter
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Engine run-on

Just looking for some help with my '67. I am having a slight run-on issue. Not a serious one, but annoying enough--basically after turning the car off, it SOMETIMES (and I stress sometimes), will "cough" one or twice afte rit is shut down.

I have read in the holley books that this is likely caused by the throttle plates being open slightly too much, but if I close the thorttle plates any more, the car will not idle. I do have a fairly radical cam-while I do not know the specs, it is VERY "lumpy" to say the least.

Is my only option to drill a 1/16 hole in the throttle plates, as the Holley book suggests?

It is already set to 14 degrees idle timing...not sur ehow much higher I can/want to go with the initial timing.

Keith
1967 Camaro
406, 10:1, comp xr282HR, Dart Iron Eagle 200cc, Holley Contender dual plane, Holley 750 DP
Muncie M-20
GM 8.5, 3.73 posi
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post #2 of 15 (permalink) Old Mar 17th, 11, 05:17 PM
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Re: engine run-on

before drilling any holes. try setting the timing at 15 or 16. Advancing just that little bit can solve the issue at times and it's less permanent than drilling and doesn't require pulling the carb.

Next choice is to make sure that the secondaries aren't opened too much. It involves pulling the carb, but no drilling required.

Brandon J. licence 1NASTY67

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post #3 of 15 (permalink) Old Mar 17th, 11, 08:39 PM
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Re: engine run-on

Quote:
but if I close the thorttle plates any more, the car will not idle.
So you have adjusted the SECODARY butterflies , got the primary idle screw and mixture screws in the middle od factory spec right?

Quote:
Is my only option to drill a 1/16 hole in the throttle plates, as the Holley book suggests?
How old is your holley book?
That is and old school practice that went out of need to do back around the late 70s.
Drilling holes is when there is no adjustment on the secondaries and even then if a holley requires it you have the wrong model spec for your engine.

Quote:
Next choice is to make sure that the secondaries aren't opened too much. It involves pulling the carb,
No there is no need to take the carb off...how to has been described many times in older threads...and how to make a suitable tool to adjust out of a rivet with a hammer.

Check out some old threads , could also be a fault in the alternator...

Quote:
It is already set to 14 degrees idle timing...not sur ehow much higher I can/want to go with the initial timing.
Quote:
I do have a fairly radical cam-while I do not know the specs
Is that 14 deg just cent advance or cent +VA on manifold vac?
you should have a ball park cent around 10 to 14 with another 8 to 10 deg all in in the VA.

My Spelling is not incorrect...it is creative

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post #4 of 15 (permalink) Old Mar 18th, 11, 04:47 PM Thread Starter
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Re: Engine run-on

OK...try to answer the questions:

The books (both recommend drilling the throttle plate:
Holley 4150 & 60 Handbook by Mike Ulrich copy-write 1980
Holley Carburetors, Manifolds, and Fuel Injection by Ulrich and Fisher, copy-write 1994

How do I adjust the secondary butterflies--I have made no adjustments to the secondaries?

Alternator is good--checked last year when I was having issues, which turned out to be an old crimp gone bad

the 14 degrees is without vacuum (hose plugged)...

Keith
1967 Camaro
406, 10:1, comp xr282HR, Dart Iron Eagle 200cc, Holley Contender dual plane, Holley 750 DP
Muncie M-20
GM 8.5, 3.73 posi
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post #5 of 15 (permalink) Old Mar 18th, 11, 05:27 PM
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Re: Engine run-on

On the pass die of the base plate is a setscrew with the slot on the bottom. Typically, one unscrews the setscrew and install it from the top, slot on the top, for easier adjustment. you can make adjustments to the screw in 1/4 turns to help lower the curb idle screw to bring in the idle circuit for a better function. Use a vacuum gauge to adjust mixture and tune for max reading.

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post #6 of 15 (permalink) Old Mar 18th, 11, 05:42 PM Thread Starter
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Re: Engine run-on

awesome--thanks everett...I suppose the carb has to come off to move the screw's slot form the bottom to the top?

Keith
1967 Camaro
406, 10:1, comp xr282HR, Dart Iron Eagle 200cc, Holley Contender dual plane, Holley 750 DP
Muncie M-20
GM 8.5, 3.73 posi
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post #7 of 15 (permalink) Old Mar 18th, 11, 06:00 PM
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Re: Engine run-on

Yes it does.

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post #8 of 15 (permalink) Old Mar 18th, 11, 09:13 PM
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Re: Engine run-on

Quote:
Holley 4150 & 60 Handbook by Mike Ulrich copy-write 1980
Holley Carburetors, Manifolds, and Fuel Injection by Ulrich and Fisher, copy-write 1994
Nether of those books ARE HOLLEY BY HOLLY

Quote:
awesome--thanks everett...I suppose the carb has to come off to move the screw's slot form the bottom to the top?
Niope
u didnt do a search
Anyway...OH it was one of Evertetts posts that talks about run on/ alternatoer problems...find it and just check

Get a rivet, flaten the end with a hammer and file off to a flat scew driver end...then put a 90 deg angle in the shaft
This can then fit up under the edge and adjust the sec butterfly
DO NOT have the sec butterfly closed p and resting against the carb bore....it must be resting ..the weight in the screw.
Adjust the idle screw ...think it is about 1 1/2 turns from closed...check the spec book
Adjust the mixture screws so in the factory spec..as above think that is 2 1/2 turns out.

Set the secondies so those are in factory spec at best idle.

Quote:
the 14 degrees is without vacuum (hose plugged)...
is that off manifold vac and what is the advance with vac attached?

All the above should be done ....noting the loppy cam you have...with a idle advance around 16 to 18 degs
But what u can have in thaty dizzy is going to depend on how many degs are in the cent and VA.

My Spelling is not incorrect...it is creative

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post #9 of 15 (permalink) Old Mar 19th, 11, 01:56 AM
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Re: Engine run-on

drilling the holes gives much more tune ability than secondary butterfly adjustment
but i have only had to do this on cams bigger than 280 @ .050 with high compression but it works very well--try timing as stated first can always put rivits in holes if you dont like it
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post #10 of 15 (permalink) Old Mar 19th, 11, 08:47 PM
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Re: Engine run-on

If your cam is very lumpy, it sure as heck needs more than 14* initial advance, if your def. of very lumpy is like mine IE cams that are at least 240-250 @ .050 with plenty of lift.
Having more initial would usually cause even more run on... Unless it's really retarded making the cylinder temps very hot and detonating the fuel.
Secondaries could be open at idle.

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post #11 of 15 (permalink) Old Mar 20th, 11, 06:24 AM
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Re: Engine run-on

idle too high
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post #12 of 15 (permalink) Old Mar 20th, 11, 04:50 PM Thread Starter
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Re: Engine run-on

As soon as she gets back from the body shop (hopefully the next week or two), I will adjust the secondaries to allow some airflow at idle, so that I can back down the idle screw, and hopefully have some more control with the mixture screws.

From what I've been reading here, and in another couple of threads,, the fact that my vacuum at idle only reads about 5-7, and bounces around ALOT, is also indicative of the transition slots being exposed at idle.

Keith
1967 Camaro
406, 10:1, comp xr282HR, Dart Iron Eagle 200cc, Holley Contender dual plane, Holley 750 DP
Muncie M-20
GM 8.5, 3.73 posi
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post #13 of 15 (permalink) Old Mar 20th, 11, 05:44 PM
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Re: Engine run-on

Quote:
so that I can back down the idle screw, and hopefully have some more control with the mixture screws.
Hmm dont rem you mentioning that above....
If that is the case...upping the idle timing a couple degrees, set the secondaries, check the accel pump gap, check float levels....(latter 2 also in some of the old posts u read)
ypu will see a huge difference in idle...and most proberly realise the cam is not anywhere as loppy as u thought.

My Spelling is not incorrect...it is creative

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post #14 of 15 (permalink) Old Mar 20th, 11, 05:50 PM
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Re: Engine run-on

had the same issue with my 355 with 280 magnum cam and 750 holley, i put a heavier throttle return spring on and no more issue!!

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post #15 of 15 (permalink) Old Mar 21st, 11, 09:41 PM
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Re: engine run-on

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Originally Posted by Nantooch View Post
before drilling any holes. try setting the timing at 15 or 16. Advancing just that little bit can solve the issue at times and it's less permanent than drilling and doesn't require pulling the carb.

Next choice is to make sure that the secondaries aren't opened too much. It involves pulling the carb, but no drilling required.
Agreed!!
may need even 18 deg. Either way you will need to work with your cent. advance afterwards.

The majority of my lumpy idle was fixed at 17 deg. all the run on was fixed.
Headers are cooler also.

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