Why is my car missing when engine is cold?

etownsley

etownsley

Streel Legal GP Race Car
When it warms up it runs fine. Is my carb float too high or too low and letting fuel leak into the combustion chambers?

I have replaced all the gaskets in the carb, manifold and head. I have also replaced the dizzy, plugs, wires, cap and rotor.

Upon startup the exhaust smells very rich. Maybe just because it is missing at startup and the fuel is not getting burned. This is why I am wondering if it is in the carb.
 
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One other possiblility.

Take a look at the mating surface between the top of the carb and the body. Over time the top will warp and allow fuel to dribble between the gasket and the barrel. As the car and carb warm up the metal in the carb expands and seals the joint between the top of the carb and body. The solution is to machine the top of the carb cover flat again to make a proper seal.

This problem also allows fuel to dribble into the engine as the carb cools and can allow flooding of the engine even though application of the gas pedal is not used.

With the car cold and at idle remove the top of the air cleaner and with a flash light or sunlight look at the seam between the top of the carb with the engine cold and idling and hot and shut down. If the problem is there you will see fuel bubbling or dripping into the barrel.

TonyK.

Grimsby Ontario Canada.
 
Thanks Tony. I will look for those symptoms.

I put brand new gaskets on the carb and manifold just last week. The carb is a new 34/34 i got from Pierce Manifolds just last year.

I can machine the gasket surface flat if that seems to be the problem.

Thanks Again!
 
Kind of obvious, but...

...is the choke set correctly (not too much spring pressure, leading to excessive choking in warm weather) and the fast idle speed set high enough?

///Mike
 
Hummm.....

I will play around with the choke. Kind of a PITA to rotate but I will give it a try.
 
Check it first

You don't necessarily have to rotate it-- check the adjustment first. With the engine cold there should be *very* light pressure closing the butterfly, but no more. If it feels like there's much resistance when opening the choke then try readjusting it.

Shouldn't be any trouble to adjust though-- just loosen the 3 pinch bolts and the center bolt; turn the spring housing a bit. Been over a decade since I've done it so my memory might be playing tricks but sure don't recall it being difficult.

Also make certain that the fast idle is set fast enough. You really don't want the engine at slow idle when it's on the choke.

HTH,

///mike
 
Mike, How do I change the "fast idle"?

Do I turn the screw in the center of the small diaphragm? I am not sure what that screw does.

Thanks!
 
I know, I know!!!

re: Why is my car missing when engine is cold?

Because it went into the house to get warm? :laugh:
 
When my son saw this thread...

while looking over my shoulder, he said, "Does the car re-appear when it's warm?"

:laugh:

Pete
 
Bwahaha!

As hot as it is here we'd have *two* engines if that were the case.

Lends a whole new meaning to the phrase "in heat".

///Mike
 
BINGO!

Thanks Tony for your suggestions! I did as you said and found the leaks you described.

First I drove the car to warm up the engine. Then I immediately took off the top of the air cleaner and started watching for bubbles around the top gasket surface. And BINGO!....as the engine and carb cooled, I saw bubbles popping out around the gasket into the primary barrel.

I will be taking the carb off next week and milling the surface flat.

As I continued to watch, I saw my accelerator nozzle dripping fuel into the primary barrel! This blew me away. I thought "how do I fix this problem?" Turns out it was simple. I just tightened up the phillips screws that held the diaphragm mechanism together. They must have vibrated loose enough to cause a vacuum leak.

The true test will come in the morning when I fire her up.

Thanks for everyone's help!

Eric
 
Good to hear you found the problem.

This one haunted my 36 DCNF for years and I stumbled on to it by error. I did just as you did, rebuilt the Carb. and installed new gaskets. Started the car and it ran great, for about a week then the old problems started again. With no aircleaner on the Carb. I was looking for a vacuum leak as the car warmed up, I noticed fuel bubbling at the mating surface of the Carb top cover. I removed the Carb top and machined it. Problem solved.

TonyK.

Grimsby Ontario Canada.
 
You know when you say it misses, I take it as one cylinder not firing for a while.
Normally when an engine has cold running trouble you don't discribe it as a miss. Cold engines run rich and smoke etc or lean and stall out. If that's what its doing, great !

The reason I say this is my experience with a few engines with a miss cold and not hot has been a head gasket leaking in its real early stages.
Hope not !!!
 
I sure hope not!

This is why I mentioned the over reving in my first post. I swapped out the head about 4 months ago.

I put the new head on with a fel-pro no re-torque head gasket. I drove it easy for 350 miles and had a race coming up so I re-torqued it at 350 miles and ran the autocross. The idle hasn't been the same since.

This is why I also questioned possibly bending a valve or breaking valve springs.

Should I re-torque the head gasket? Or is it too far gone?

Thanks for your comments!

Eric
 
My thoughts are just from a far ...

If it seems to be one cylinder I would isolate it, find out which one it is.
Surely prepping a cold start up maybe by loosing up the plug wires so they are easy to dislodge, testing for each cylinders contribution. Clearly the one wire you dislodge/pull off that triggers no change is you goal to find. From there, well that's another post.
You may be able to smell something a little different in the exhaust at cold start, or you might be able to remove the coolant pressure by taking off you pressure cap, start the engine to clear anything in the cylinder and wait for a fresh cold start the next day. It may not leak as much liquid in the cylinder and not miss.
Clearly this is all assuming the worst and might not help a bit LOL but may tell ya something.
 
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