Car running poorly when cold

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smrcuda

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I have a 68 cuda with a 340. It seems to have developed a problem when it is cold. It seems to be missing and nearly stalls out. Here is the challenge.
Once it warms up it runs just fine. The choke is working correctly. I have had the same carb on when it ran Ok for me. I did change the insulating gasket but there was no change. I really think it is an electrical problem. I has electronic ignition. I recently put a chrome powermaster alternator on it.
It would be easier to figure out if it ran bad all the time.
Does anyone have a suggestions?
Thanks for the help.
 
Do you have a stock or aftermarket intake? Some of the aftermarket intakes have no heat crossover under the carb and that will make the car run bad in cold weather. If you have a stock intake and exhaust manifolds either the heat crossover is plugged and/or the heat riser in the exhaust manifold is stuck. These are just a couple of old problems that we used to deal with in the days of carburetors. Cool, moist climates need heat or the carb ices up.
 
I have an LD 340 intake and the car has headers.
I did check the distributor and it was dry.
Keep the suggestions coming. I'm sure we can figure it out.
 
What type of carb do you have on there? I run a Carter AFB on a LD340 and have the heat crossover blocked. I've run this 360 in the COLD Canadian winters at -30C and it would warm up enough to drive in about 15 minutes with no missing or stalling.
 
It has a edelbrock carb. The heat crossovers are not blocked.
It was running OK at start. Something changed.
 
Have you changed spark plug makers lately. I had a 360 that ran like crap on the Champion plugs called for and fine when up to temp. I went up one heat range and problem went away.
 
smrcuda said:
I have a 68 cuda with a 340. It seems to have developed a problem when it is cold. It seems to be missing and nearly stalls out. Here is the challenge.
Once it warms up it runs just fine. The choke is working correctly. I have had the same carb on when it ran Ok for me. I did change the insulating gasket but there was no change. I really think it is an electrical problem. I has electronic ignition. I recently put a chrome powermaster alternator on it.
It would be easier to figure out if it ran bad all the time.
Does anyone have a suggestions?
Thanks for the help.
Click to expand...

I had similar problems with my 318 Valiant last winter. It stalled and missed heavily when it was cold, but ran just fine after warm up. I found out that my old ECU was bad: changed to a new one and it solved the problem. It is also possible that ground contact between the ECU and frame is bad: should be metal-to-metal.
 
I think it could be the ECU or the ground. I will check it out.
I will pull the plugs and see what they look like also.
Thanks for the ideas
 
I worked on the ground on the ECU last night and it seem to have sovled the problem.
I am going to pul plugs and check the gap.
Thanks eveyone for the help
 
Thought I would add my two cents worth...I'm not sure where you live, however as stated temp change and dampness can be a big problem for some. I had three different vehicles and they "all" had problems like you stated (mostly late fall until early spring). The majority of cars on the road have heat risers off the exhaust to worm the air going into the carb.

When "I" changed out my vehicles engines to headers and a "open" face air filter as K&N. The air flow was now no longer heated and thus going through the carb vanturi which caused the mixture screws to freeze (Iceing). In turn, the engine would not idle correctly and stall out. NOT thinking...being a Canadian..dah...I was wondering how other guys got away with such a problem :scratch: and contacted a speed shop in San-Deigo California. They never heard of such a problem..(they were all completely lost) :shaking2: . Understandable, never gets cold enough down there to have a iceing problem.

All I do now on colder/damper days is to flash the engine and wait until it stalls (2-3 min during iceing). Wait another 2 min until the slightly heated block worms up the carb area, then re-flash and go without any more problems.

PS - Confirm if iceing is your problem by flashing the motor to see if your mixture screws turn white (frost). PSS-I was also "told" that a guy can now buy a carb adapter plate that has a relayed electrical coil that heats up the air flow into the carb for the first 5 min when starting?
 
Engine running great now. I put a new ECU in and it seems to be just fine. I am going to put the old one back in to see if it wasn't just a grounding problem.
 
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