Idle problem similar to falcon fanatic

[dmsmith55]

I am having almost the same problem as falcon fanatic had. Car was running great one weekend, then the next time I go to start it, no idle less than about 2000. At the time I had the progressive Weber on a Clifford adaptor. Thinking it might be the carb, and since I have one of the new heads ordered and would be going to a Holley anyway, I went ahead and got one. Just today started it up with the Holley 500 2 bbl and it acts exactly the same. Will start if I hold throttle open. Will run if I screw in idle screw enough to maintain 1800-2000 or more. Sounds good at that speed, no miss or popping. Will rev OK from there up. When I try to idle down, it gets to a point where it just quits, then tries to run backwards and spits back out through carb, no fire just gas, exactly same as happened with the Weber. Perplexing. I don't see it being two bad carbs. I thought vacuum leak too, but don't find one. Any ideas????

 

[ludwig]

Timing? Just an idea.

 

[Bort62]

Well basically if it's not a vac leak it has to be the timing.

Asssuming you didn't burn an intake valve.

Do you have points or electronic ?

 

[Mercury Mike]

TIMING!

 

[dmsmith55]

Bort62: I have the DUI distributor. I have been thinking cam timing for some time now also. Ignition timing changes don't really have an effect.

 

[dmsmith55]

Also thinking something happened to an intake valve.

 

[dmsmith55]

Compression test was about 170 on all 6. Rules out bent or burned valve or major slipped cam timing. I also put dial indicator on #1 intake rocker just to check and it was real close to cam card on intake opening. IIRC, open 0.006 at 10 deg BTDC. Hard to check all 6 as no good place to stick magnetic base.

 

[falcon fanatic]

On mine it turned out that an internal passage in the carb had lost a lead plug and was creating an internal vacuum leak. The rebuilder is pluggin it with epoxy instead. Yours sounds exactly like mine, right down to the "cough of death" vaporous backfire. Unless you have two screwy carbs (unlikely) then you must have a vacuum leak. After all, why would your timing suddenly drift so far as to cause this problem? I presume you've tried the starter fluid trick, right?

 

[dmsmith55]

falcon fanatic: I used WD40 with no luck. I may take carb back off and check all gaskets and try again. Strange, though for it to behave same with two completely different brand new carbs on different adaptors, etc..

 

[Bort62]

Look for cracks in the intake log.

 

[Bort62]

Or a bad PCV valve, Brake Booster, etc - all vac devices are suspect.

Disconnect everything that uses vaccum and plug the ports, see if it runs better.

Bad Vac advance can could do it, too

 

[falcon fanatic]

Yes, strange. I imagine it's not the actual carb. Also, I doubt WD-40 will work for this test.
Definetly remove all hoses and plug all vacume ports. If it suddenly idles, then you know it's one of those. Otherwise, try actual starter fluid. Even if you have it "idling" around 1800 rpm or so, you should still be able to kill it with the starting fluid if there is a leak.

 

[dmsmith55]

A HEI module from Auto Zone cured my problem, same as falcon fanatic...he blazed the trail.

 

[falcon fanatic]

That's funny, although not in a ha, ha kind of way. I'm beginning to wonder about this decision to plop the big bucks down on the DUI. I like the concept, and I like the performance, but this reliability issue is not good. Is this common to all GM HEI igitions, or just the Performance Distributor brand?

 

[Lazy JW]

I have driven many hundreds of thousands of miles in several Chebbies ignited by GM's HEI ignition with zero problems. It really is a very good system: cheap and reliable. Ford took way too long to catch up.
Joe