Idle high

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tekslk

tekslk

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Ever since I installed a comp cam in my car I have to keep idle at 1200 to hold 800 when I put it in gear, My vacume is low and im wondering if I added a vacume canister would this help idle better? Also if it would how do you hook the canister up? Timing and tune are great just the little idle problem.
 
what cam? Degreed?

If it drops that much there is something wrong.
 
Unless it's a 360 with a 260 @ .050 cam there is no reason for it to idle at 1200 rpm.

If it's sized like a 403 voodoo or a XE268/274 it should idle at 800-900 max with a minor drop in gear.

Sounds like a vacuum leak somewhere. Power brakes? Makes sure it's sealed up well on the intake/carb flange. sometimes there can be a very minor interference which causes thing to not set properly.

Another is to disconnect EVERYTHING vacuum related from the carb, plug it off and start it up. See if the idle can be turned down and if the drop in gear improves.
 
It is a 360, 2800 converter, idle consistant just the big drop, would a canister help or am I just spinning my wheels.
 
idle circuit too lean and or more initial timing vac canister wont help at all
 
Thats a LOT of initial timing, but your problem sounds like a vacuum leak.
Good Luck.

George
 
You put a cam in and don't know what it was? You need to get that info first. but... It takes a huge cam to run as you say. Like George said, it sounds like a vacuum leak. Pull the intake, make sure it fits properly, and replace the gasket.
 
this very well could be a big vacuum leak but when you have a vacuum leak it is hard to control the idle down because when you tune your idle mixture it will partially compensate for the lean air leak and idle it up pretty fast. can you open your mixture screws and have the engine slow down from being to rich? if you can then i would go with the vacuum leak and or some funny cam timing. did you degree the cam? one other thing about a manifold leak. sguirt some carb spray or something like that around your manifold and carb and see if the idle changes speed before you pull the manifold. if its leaking it should suck that stuff in and make it change your idle speed. if its leaking on the outside. if its leaking on the inside you should be getting smoke out of the tail pipe from sucking oil in. and if its leaking but not sucking oil in there would be suction on your hand if you block the breather and disconnect your pcv valve. just some thing to check! 19 initial isn't that big of a deal not too high in my opinion seems to be good.
 
A long duration cam will take more initial timing so 19* isn't unusual. What carb? Holley? With the idle speed cranked up you may have too much of the transfer slot exposed which means you're out of the idle and into the transfer circuit of the carb too. Can you put your hand over the carb while it's running and kill the engine?
 
I have the same cam in my Fmla S and I used Rhoades variable duration lifters. They bleed down at idle and pump up by 3500 rpm. I can get mine to idle at 800 rpm.

I am also runnning the MP electronic distributor with one light stock spring and one of the light MP recurve springs with no vacuum advance hooked up to the dist. I run 17° adv at idle and 35 total at 2500 rpm.

Rhoades lifters may help you (more than a cannister). They take out 15° duration and .025" lift at idle. They don't bleed down above 3500 rpm and give the full lift and duration of the cam at high rpm. I have been using them for over 25 years and put over 250, 000 on them without any problems. They work better than the other competitors variable duration lifters.
 
I had the same issue, because I had replaced the base and gaskets of the carburetor/intake with thicker versions so because it was taller the throttle cable was throwing the idle off. Stupid mistake that I overlooked. Thank guys for the clear insight always turns out to be some thing small and simple.
 
You havent posted your idle vacuum reading yet. Nor answered the question about vacuum advance hook up.
Make sure the vacuum advance isntworking at idle.How about throttle cable adjustment? Vacuum lines can be pinched off, one at a time.
Your combo should easily idle down to 850ish,and make near 11 inches vacuum, with your current mechanical idle-timing of 19*.
I suppose you took the intake off to replace the lifters, right? Was the carb removed from the manifold?Did the carb receive any adjustments other than idle speed, between cams?Any chance the gasket(s) got tweaked during the manifold re-install?
Just for curiosity sake; what did it idle at with the old cam and what were the cam specs of that old one?

A vacuum canister is a vacuum storage device. It stores vacuum created during times when the engine is making high vacuum, for use by vacuum operated devices ,later, during times of low vacuum.It does it automatically.It also acts to smooth out any vacuum pulses. It is most often used to help the power brakes function at stoplights when a big-cam engine is idling and not making enough vacuum. Other devices that can benefit are; A/C controls, certain emission devices/timing controls,vacuum headlamps,and pretty much anything that depends on a constant source of vacuum to operate.
It could be used to kick your vacuum advance in at idle,but theres not much benefit in doing that on your combo.Your cam should make enough vacuum to power the booster.I had a 292/509 that was no problem.
 
This thread is three years old. BIG-B went through and updated a bunch of old threads last night with the same helpful post.
 
It's always good to update old posts everyone has same issues everywhere everyday.

Good for noobs like me.
 
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