She'll rev fine, but idle...Not so much!

alphamale1906

I installed some 305 heads on my 69 Camaro block (350) and yes, I've read all the threads about the pros and cons on that one! But, just when I thought everything went well with that decision...BAM! I can't get the thing to idle. She sounds great when running (either from feathering the pedal or revving over 1500), but no matter what, I can't get it to idle. I've got a Holley 600CFM ontop of an Edelbrock dual plane manifold. I'm running hydraulic lifters, that I must have checked for zero lash at least 5 times before firing.

I've tried multiple carb adjustments. Mixture screws from 3/4 out to 5 or 6 full turns out (going in 1/4 turn increments) and still no idle. I'm afraid to push the upper limits of timing to keep her running. However, if I drop timing down to 3-8 degrees BTDC, then I do experience very light sporadic back firing, just before she stalls out. Yet, if she revs above 1K to 2K no issues. In order to loose the backfiring and rev without hesitation, the engine prefers quite a bit of advance (around 16+ degrees).

I've plugged everything, so I'm confident about no vacuum leak. Is it possible the valve lash may be set to tight?

I'm sure my compression is in the upper atmosphere! But. I went with a thick head gasket to take a little bit of the high compression edge off and I'm running a slightly cooler plug and high octane to help with detonation.

When reving her (and hopefully not wiping my cam), she sounds fine. But she just won't idle without constant feathering.

I've tried advancing the timing, but I'm to the point where she'll barely turn over from the compression and timing advancement.

Any suggestions on the problem? I've torqued everything to spec and used FelPro gaskets everywhere.

Evil or Very Mad

Thanks!
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CANTED · Posted: Fri May 02, 2008 8:41 pm Post subject: no idle

It sure sounds like a vacuum leak, I know you said you plugged things but it could be a manifold gasket. Also, is the carb new? A leaking power valve could have it so rich that it will only run with the throttle partially open. Just what came to mind, good luck with it.
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464elky · Posted: Fri May 02, 2008 9:27 pm Post subject:

I'll just throw in that the idle circuits may be stopped up and just won't give it any fuel until you get off the idle and transfer circuits. Sounds like to keep it running you are using the accelerator pump to keep squirting some in.
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Elky 83 · Posted: Mon May 05, 2008 7:44 pm Post subject:

Higher torque converter??????? 2500 t0 2700
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alphamale1906 · Posted: Tue May 20, 2008 9:32 am Post subject:

First and foremost, let me just start by saying thanks to all of the suggestions!! Finally got the thing to idle, but I'll go through my brief check list....

1) Checked hoses on the top side but not for the vacuum leak at the transmission modulator (hose was disconnected there)
2) High compression heads just a pain to dial in with so many other issues (305 heads on a 350 yeild HIGH compession!)
3) Crappy gas left in the car from God knows when...Made the mistake of just adding high test before drainig what might have been in the tank
4) lifters were too tight and needed to be adjusted after motor warmed up
5) Timing was off considering high compression and crappy gas

Anyway, got her to idle after several weeks of line by line trouble shooting.

Thanks again for the suggestions and help!!
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Excuses are the tools of the incompetent!