Carbed L69:

When cold, the car starts fine, very easily, almost instantly.

Idles fine when cold, responds to throttle somewhat. After car is warm, just barely warm, the idle rises to about 1500 and won't come down, unless to stall.

If you accelerate the engine and left off of the throttle, after the car is warm, the idle won't catch, it just stalls.

When warm the acceleration is very poor, and in fact will often kill the car.

Timing is set at 8*, wires and plugs are new, has a vac advance HEI which worked fine before cam swap, have had the same exact consistent problem with 2 different carbs.

The problem appears to worsen after warming up, so I don't think that it is something in the valve train....am I wrong?

What could it be? Please Please Please help.


I've checked plugs, have some carbon build up.

Some black smoke at start up.

 

check fuel pressure at the carb...
may be getting too high.

what pump do you use?

 

Sounds to me like a BIG vacuum leak...

If the fuel pressure was too high, you'd se gasoline coming all out the top of the carb. If it isn't doing that, then the needle valve has control, and the fuel pressure is OK.

All your symptoms scream "lean" to me, which is of course what a vacuum leak creates: too much air, not enough fuel. You just put on a new intake IIRC... Do you have the right carb gasket? All the vacuum supply (there's an oxymoron for you - "vacuum supply") holes plugged up? All the hoses connected at the other end? Intake gaskets OK? Try some carb cleaner in a can, shoot it at places that might leak, see if it affects the idle speed; if you find a place that it does, you just found your leak.

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"So many Mustangs, so little time..."
ICON Motorsports

 

I don't hear a leak anywhere, but I will look. I still have the stock mechanical fuel pump.

How would I tell if there is a leak in the intake gasket?

I don't think it's the carb, because like I said, I tried the stock cc carb and a holley double pumper....same problem.

Having a problem with the intake gasket is likely since everything else seems to pan out.

 

so what was the fuel pressure?
and what pump you run?

 

oh yeah, you have a computer controlled carb..

nevermind

 

Take a look at the pcv valve grommet make sure it is a sealed fit in the valve cover and that the pcv valve fits snug in the grommet and also check the hose from the pcv to carb for leaks.

 

I would check the choke. Choke, sounds like it's not openning to me. Just trying to think of the simple stuff.

"Oh yeah, well i'm taller"



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89 RS Conv 305 700R4
85HO heads
Edelbrock intake
Holley 600
Hedman Hedders and Y pipe
Flowmaster
B&M MegaShifter

 

Chevywolf,

With the history of the components on my car, I figured it maybe a carb problem, so I swapped the carb out.

The first carb has a choke, the second one doesn't.

I guess what's so frustrating about these types of problems is that you have to try so many different things to figure them out, that it takes a ton of unfruitful labor and in the meantime your frustration mounts.....

Any other options?

I was thinking of changing the ignition module and the plugs again, but if the ignition signal was weak, why would the rpms elevate when the car warmed up?

 

I'm zeroing in I think.

I replaced the condensor in the distributor. That's all I've changed so far.

Now the exhaust is mostly real clean, but then ocassionally, it'll spit out some soot. You probably wouldn't notice it unless you hand was under the exhaust.

I'm going to swap out the coil and ignition module along with another set of plugs (these are fouled badly) and see what happens. Wish me luck.