Idle acting weird - Team Camaro Tech
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post #1 of 20 (permalink) Old Jul 4th, 09, 01:49 PM Thread Starter
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Mike
 
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Idle acting weird

My Holley carb idle was a bit too low, 600-700 rpm in park.
So I adjusted the idle speed screw to bring it up. It came up too high to 1500.
So I backed it off again and started making tiny adjustments. I was going for 800-900 rpm in park or neutral.
I'd adjust, rev it, adjust rev it and with each tiny adjustment, it came up a tiny bit but not enough. Then after several tiny adjustments it comes way up to 1500 again.

I can get about 700 rpm or 1500. I can't get it to a middle ground.

What's going on with this? What should I look into?
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post #2 of 20 (permalink) Old Jul 5th, 09, 07:36 AM
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clayton hicker
 
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Re: Idle acting weird

mabe a vacume leak?when you set idle up is it moving the secondary throttle shaft also?

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post #3 of 20 (permalink) Old Jul 5th, 09, 10:20 AM
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Charlie
 
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Re: Idle acting weird

WJen you are making the adjustments is the throttle linkage disconnected? I ask because I found that with the rod in the throttle arm, there is only so much turning of the screw before the arm can't go back anymore because the stud is contacting the rear of the arm hole. You try to make small changes, but when it contacts the back of the arm hole you have to turn a little hard and that makes it jump up too high. Try making the adjustments with the throttle rod separate from the carb. Just an idea.

Charlie Knudsen 67 Camaro RS/SS 350 TKO 600, 4.10's, AFR 195 Street Heads, Comp 270H, Rhoads Lifters, Crane Ignition, Pertronix Dizzy, Performer RPM Q-Jet, Heavily Modified Q-Jet, Hooker Comp Headers, MagnaFlow 2 1/2", 144 Decibles(Alpine CDA-7998 Head Unit, RF X7 and RF 750X Amps, MB Quart Mid's & High's, Kicker L7 12" Solo Barics)
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post #4 of 20 (permalink) Old Jul 5th, 09, 02:02 PM
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Re: Idle acting weird

Set the idle screw to about 1 1/2 turns from bottom...then adjust the sec stop scew and mixture screws to your rpm idle.
Fine tune on the idle scew and mixture scews

OR it could be a too light a spring on the cent advance, that starts coming off at the slightly higher rpm.
Or a vac advance that doesnt activate at the low rpms, as u slowly increase rpms, the vac increases and activates ...increasing advance...increasing rpms.

My Spelling is not incorrect...it is creative

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post #5 of 20 (permalink) Old Jul 5th, 09, 05:25 PM
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Tim
 
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Re: Idle acting weird

I second the advance issue. Have you watched what the timing does as you play with idle speed?

Tim Smith
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post #6 of 20 (permalink) Old Jul 5th, 09, 07:10 PM
David
 
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Re: Idle acting weird

The vacuum advance is my bet. Your vac advance is probably connected to a ported vacuum source.
As you increase the throttle opening, you are starting to get vacuum on that port which adds vac advance and increases your idle speed.
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post #7 of 20 (permalink) Old Jul 5th, 09, 08:28 PM
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T
 
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Re: Idle acting weird

Quote:
Originally Posted by DRIVESHAFT View Post
The vacuum advance is my bet. Your vac advance is probably connected to a ported vacuum source.
As you increase the throttle opening, you are starting to get vacuum on that port which adds vac advance and increases your idle speed.
Ya, that's what I was thinking too. Try moving the vac advance to a full-time vacuum source, and try to re-adjust. Moving from ported vacuum to full-time vac should bring your idle speed up to 1500-ish, then you can back off the idle speed screw to get it back down...
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post #8 of 20 (permalink) Old Jul 5th, 09, 09:31 PM
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Re: Idle acting weird

If the VA is attached to ported (above butterflys) and it is the VA, then the idle screw is being opened to far, which indicates the sec butterflys are to closed... see my post above.

remove the dizzy cap, attach a vac pump and gauge to the VA, put your finger in the end of the advance lever, suck...note at what vac the lever pulls the dizzy mechanism.

put a Vac gauge in the manifold vac and establish what the idle engine vac with VA disconnected...

If the VA is connected to manifold vac, the VA should be all in at about 1" above the idle....

My Spelling is not incorrect...it is creative

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post #9 of 20 (permalink) Old Jul 6th, 09, 04:17 PM Thread Starter
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Re: Idle acting weird

Sorry, just got back from a river rafting trip that almost went bad. I'm beat up now.

OK so you guys are on the right track because my VA is not attached to full manifold vacuum. Its on a port on the primary metering block.

I will move that tonight when I get home!

Then I will report back with the results....

Thanks!
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post #10 of 20 (permalink) Old Jul 6th, 09, 08:53 PM Thread Starter
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Re: Idle acting weird

OK,

So just some more information for you that I might of left out.
Moving down the VA line of thought, I probly forgot to mention that I have a big cam and at idle, I've got about 5-6 inches of vacuum.

At 1500 rpm, where it seems to like to go when I mess with it, there is better vacuum. Like about 12-15 inches.

I have a Edelbrock Victor 454-O manifold. It doesn't have a manifold port for vacuum. The closest I can get is the base of the carb very near the manifold.
Will that do for vacuum? I already have a larger 3/8 line coming out of there to a vacuum canister for brakes. I could tee off of it.
Will that do?
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post #11 of 20 (permalink) Old Jul 6th, 09, 09:05 PM
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Re: Idle acting weird

either of those will work, and another option is to put a carb spacer that has a pipe port, if you have hood clearance to add a spacer. You could also tee off tranny modulator source. Vac can doesn't consume, so it won't affect the operation of anything.

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post #12 of 20 (permalink) Old Jul 6th, 09, 10:10 PM Thread Starter
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Re: Idle acting weird

Quote:
Originally Posted by 77wolf10.85 View Post
either of those will work, and another option is to put a carb spacer that has a pipe port, if you have hood clearance to add a spacer. You could also tee off tranny modulator source. Vac can doesn't consume, so it won't affect the operation of anything.
The only time the vacuum canister consumes is when I hit the brakes. But there is check valves in a vacuum canister right? So it should only effect periodically right after I apply brakes right?

As far as hood clearance, I'm gonna need to see, if there is any clearance, its very little, I do have a spacer in there I think, perhaps I could replace it with one like you mention.
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post #13 of 20 (permalink) Old Jul 7th, 09, 07:24 PM
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Re: Idle acting weird

drill and tap it if you already have one and it doesn't have an allen headed plug in it already

as for vac can consuming when you hit brakes, think about what happens right before you hit brakes,,,,,cruzin along and some idiot pulls out in front of you and you get off the gas to go for brakes,,,vacuum rises(actually pressure falls) to highest it ever will in those conditions. Vac can is pulled like a bastard and has negative pressure on the order of way over 20"HG( about negative 10#)with a mild cam, you hit the brakes and your booster consumes vacuum, which the little vac advance can has actually stored a tad bit of for you. When the booster consumes vacuum, pressure will actually rise somewhat(lower vacuum is higher pressure )(you are equalizing atmospheric to manifold vacuum) but I doubt you could see it on most gauges because the pistons sucking against the closed butterflies at high speed would replenish it in the blink of an eye. And really, the pressure equalizing doesn't happen until you let OFF the brake anyway, because the booster is just a bigass vac reservoir with check valves that uses that pressure differential to YOUR advantage.

Tim Smith
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post #14 of 20 (permalink) Old Jul 7th, 09, 09:45 PM
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Re: Idle acting weird

Quote:
as for vac can consuming when you hit brakes,
Exactly as described above is what happens in the REAL world
The only time it maybe an issue, is idling out of a gas station or driveway, tap brake 1st time, is ok cause of trapped vac in the brakes, but 2nd time...and rem you are travelling about the speed of a mother and pram, the brakes only have parial vac, and are harder...
and u stop nps.
Now apply this to the real world, it is very rare one touched the brakes twice, at idle speed after pulling away from the pumps and slowing down to check the traffic....and IF u do, it just means u have manual brakes at 2 mph.

My Spelling is not incorrect...it is creative

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post #15 of 20 (permalink) Old Jul 8th, 09, 10:28 PM Thread Starter
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Re: Idle acting weird

Quote:
Originally Posted by Steptoe View Post
Exactly as described above is what happens in the REAL world
The only time it maybe an issue, is idling out of a gas station or driveway, tap brake 1st time, is ok cause of trapped vac in the brakes, but 2nd time...and rem you are travelling about the speed of a mother and pram, the brakes only have parial vac, and are harder...
and u stop nps.
Now apply this to the real world, it is very rare one touched the brakes twice, at idle speed after pulling away from the pumps and slowing down to check the traffic....and IF u do, it just means u have manual brakes at 2 mph.
Manual brakes at 2mph I can live with.
Just not at cruising speed.
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