Hello,
I have a 455 with a voodoo 262/268 camshaft. I really like the low and mid range, but the idle is rougher than I like.

Timing is 35 total + 12 vacuum (manifold). Stock quadrajet, about 17in Hg of vacuum at idle. There are times when the idle is fairly rough and others when it smooths out. Something is inconsistent and I'm not sure what it is. Richer idle seems to help (seems to run best at around 12:1, but I'd rather not run that rich). Any ideas how I can smooth it out?

Thanks.

 

Check for vacuum leaks, could cause erratic idle as the engine goes from cold to hot.

 

That’s definitely a mild cam, it should idle pretty smoothly. Start with the basics, make sure you don’t have a crossed plug wire, dead cylinder, vacuum leak, etc.

 

Try an advance curve kit. I assume it is running low base timing like a points ignition? If you don't want to run more vacuum advance, recurve so there is less mechanical advance and more initial timing at idle.

 

I agree, it's what I did with the 217/221 cam in my 350 and it really smoothed the idle and made it more responsive.

 

I will check for vacuum leaks.

Engine now has a HEI distributor. 20deg initial, 35 total. So plenty of initial.

Thank you all.

 

Qjets are known for having excess wear on the throttle shaft bores, creating vacuum leaks. If it has not been repaired with shaft bushings in the past, I'd check that.

 

I sprayed ether all around the intake and base of the carb. Also sprayed around the throttle shaft area, which did have a bit of slop. No changes in idle that I could notice.
Thanks.

 

Maybe provide a video (audio) of the engine idling if possible. It could be that your definition of "rough idle" differs from ours.

 

Will do.

My problem is that it makes the car shake, which is annoying. I have an old truck with a Cummins 4BT (engine known to be very uncivilized) and it is silky smooth in comparison.

 

My G-block shakes the fenders a bit with its Comp Cams XE262H (218/224 @ 0.050, 0.462/.469 lift, 110 LSA). I theorize that it may be because of the long stroke (which your 455 shares).

You get used to it.

 

The strange thing is that it is inconsistent. I want to find the conditions under which it doesn't do that and replicate them.

 

Sticking valve(s)? You stated you have 17" of vacuum. Is that steady, when the idle is smooth? What is the vacuum and needle condition during the rough idle.
Perform a cylinder balance test while the rough idle is occurring.

 

Then something is out of balance. It has absolutely nothing to do with the long stroke.

 

Well, there goes that theory. Thing runs fine off idle and the shaking is pretty mild so I'm not going to tear it apart just now.

 

How about take a timing light and hook it to each spark plug wire while it's running rough. Point the light at the underside of the hood and look for consistent flashing without any stuttering. Do that for all the plugs. If any stutter than it could be an ignition problem. If you don't see any stuttering (missed flashes) then at least you know it's not due to an ignition problem.

 

The primary shaft in my quadrajet had quite a bit of play. I addressed that and I saw a great improvement. It likes to idle at around 13:1 A/F (a bit rich for my taste, and might hint to other vacuum leaks), but it is quite acceptable now.

 

I’m gonna suggest that unless your Qjet is modified (idle air bleeds, etc) and optimized, you’ll have trouble getting the idle consistent, even with a relatively small cam like that. If there are no vac leaks presenting themselves, my guess is that it’s internal calibration. That cam is still way bigger than what that carb was calibrated for.

Doug Roe, Cliff Ruggles and Ken Gies (occasionally on this site as “techg8”) all have books available if you feel up to the task of modifying.

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