CVO2FIXUP

Hey all, was out for my first and last cruse of the year just north of the city. ( I just bought the car ) 71 BB 4 speed. All stock with stock carb. Car ran like a clock. When I got back in to the city and hit some stop and go traffic the car started to sputter a bit when creeping forward, just off idle as the clutch was released the engine would want to die, I would have to pull in the clutch and pump the throttle to recover it. Well as the temp increased ( slow going traffic ) the idle dropped to a rough 600 rpm and the car would stall as soon as you release the clutch and try to move. Once started the car would run OK for about 15 seconds then the idle would drop again. As the temp got even hotted the car stopped idling all together. Would start back up, sputtering and coughing. After the sputtering and coughing I could rev it up and it would rev very well. I can get it moving and at speed the car ran as smooth and perfect as it always does. As soon as I came to a red light and pull in the clutch the engine would stall. Very hard to start back up again with lots of sputtering and complaining. Could see black smoke from the exhaust when sputtering and trying to start and would clear when started and revved up. So it seems as the temp rises the worse it runs. Finally got to where I was going and let the car sit for about 45 min. Restarted very easy and all the symptoms went away. ( car cooled down ) Is this a problem that seems familiar to any one? And what should I focus on first. Vette is practically unusable with this problem. P.S. I am in Canada and it was about 14 degrees ( 40 Fahrenheit ) So not to warm out side. I can imagine how it will be in the summer. Any help would be appreciated. Thanx Ernest.

MajD

Black smoke happens when the car has too much fuel in the mixture. Based on that, there are a couple things that come to mind. It could be choke isn't working properly and stays engaged, your air-fuel mixture needs adjustment, or both.

CVO2FIXUP

I thought it could be the choke as well. Can the choke come on, get activated when the engine is hot? This happened when I sat in traffic for a very short period of time. And did not go away until the car cooled down after 45 min. If its the choke that would be a easy fix. Could this be vapor lock?

doorgunner

Vapor lock.......(fuel "boils" inside carb because of coolant being unable to keep the engine at normal operating temperature which could be caused by several things)

or.......sloppy choke.......(choke plate blocks off air to intake)

or......failing module inside distributor....( spark gets weaker to the point engine loses power or quits running)

Those are the things I have read about and dealt with in the last two weeks with my engine. It had all three problems which had a rookie like me running in circles.

CVO2FIXUP

I would be the rookies assistant LOL. That's how much I know about cars. Ok, maybe not that bad.

Did you have the problem of stalling and very hard starting when hot? I drove this car a hand full of times and always on the open road. Never had these symptoms before. Today was the first time in traffic and the thing just fell flat on its face. I need to figure this out. Can the choke come on when the engine is hot? The distributor is a fresh rebuild. So it's like new. Most likely the carb. I guess.

LB66383

I doubt it is vapor lock. That happens when the fuel vaporizes in the fuel between the tank and the fuel pump and the pump ends up not supplying fuel anymore. In that case, the engine normally dies and won't restart until things cool down. Your problem definitely sounds like the fuel is overflowing the carburetor and flooding the engine. It could be the needle/seat isn't cutting off the fuel flow into the carb, or the carb body is getting very warm. If the carb and rest of the fuel system is in good shape, 40*F weather shouldn't cause any heat problems unless the engine is running very, very warm. The fuel system -- tank, lines, carb -- could have 43 years worth of dirt & silt floating around in it that isn't helping the carb function the way it's supposed to.

briankeery

Since the car is probably laid up now for the winter, why not contact Lars and inquire about getting things looked at? He'll be able to narrow down your problem very quickly.

Mashman

Another thing to consider is the ignition.

A bad coil can cause the above problem. Also, bad, loose or frayed connections at the starter or coil can cause the same issue also.

Mike Ward

What you describe sounds more like percolation, not vapour lock. Percolation is the fuel boiling inside the carb and flooding the engine. Given the cool weather, that's not likely.

Possibly the former owner installed the wrong fuel pump giving too high an output pressure or the needle and seat on the carb float are leaking or stuck.

Start the engine again and look for fuel dribbling inside/outside the carb to confirm.

REELAV8R

Does you vette have the exhaust heat riser on the right manifold? If it does check it for proper operation. It should be open once engine warms up.
Sounds like too much crossover heat to the manifold and like mike says percolating your fuel.
Could also need a thermal spacer between carb and manifold.

CVO2FIXUP

Thanx for all the possibilities. Wrote them all down. Will attack this problem next spring. Just funny that it happened when the car got warm. One time it backfired through the carb as it was stalling at a red light. A hole bunch of white / light blue smoke came up from under the hood. This happened right beside a packed buss stop, in front of every one. Very uncool feeling. So any more assessments would be great. And how do I get a hold, or contact Lars? Is there a web site for him? Thank you guy's.

CVO2FIXUP

Hey all, a member hooked me up with Lars contact info so I e-mailed him with my query. Lars was gracious enough to read my long winded e-mail and respond with some great suggestions. All of which I will asses to track down my warm condition stalling. Here is Lars response to my e-mail for all to see, and take away from it what ever might help others. Cheers Ernest.


Ernest -
Troubleshooting drivability issues via e-mail, without seeing the car and touching it, is completely impossible. The following issues can cause the problems you describe, but these are not the only issues that can cause the problem:

Bad coil
Bad points
Incorrect dwell
Bad condenser
Bad vacuum advance control unit
Dirt in fuel tank pickup sock
Pinched fuel line
Defective fuel pump
Plugged fuel filter
Debris in needle/seat
Sunk float
Defective choke components
Vacuum leak (can be caused by leaking accessory)
Bad fuel

Narrowing it down requires a physical inspection of the car with appropriate troubleshooting to determine where the actual problem lies. I'll put 80% odds that it's one of the issues outlined above...

Lars