Engine Dies Out When Hot

So at first I thought my '68 died only while in gear and when fully warmed up. But now I see that it doesn't matter whether it's in gear or in Park/Neutral. In Park with the engine running at idle, after it fully warms up, the engine starts having an erratic idle then eventually dies. Then it won't start until the temp of the engine drops down a bit.

So my guess is this is definitely not a vacuum leak, it's just got to be something with the carb. Could there be too much heat being transferred to the carb. I see a gasket at the base of the carb separating it from the intake manifold, so doesn't look like a lack of insulation problem.

I know it's not a vacuum leak, because with the choke fully open I put a rag slowly over it and the idle never
increased. It did drop as I covered the choke more though, as expected.

Any other ideas?

Steve

This is a long shot, but I have seen it a few times. Sometimes the condenser inside the distributor or the one by the coil, if equipped, will cause this. Even less often, the ignition coil itself. Both of these are fairly rare. Check the car for spark when it dies and won't start, then go from there.

Ken Styer

My 76 was doing something similar last year. after replacing the thermostat, replacing the ful pump, rebuilding the distributor, the actual problem was the fuel line... Whenever the engine got hot, the heat would colapse the fuel line because the rubber was weak. Once the engine cooled, along with the fuel line, she would start right up. Check your fuel lines. If they are more than 7 years old, I would replace them...

Thanks. But mine are steel. The only sections that are rubber are at the back of the car at the fuel tank. There are some rubber lines near the fuel filter but their small sections and no where near the exhaust manifold. Can steel lines collapse when hot? I don't think so. But maybe?

Steve

No, if yours are steel, it's definitely not the lines, they wouldn't "un"collapse as they cooled, and that would take a LOT of heat anyway. I would seriously consider a carb rebuild, or, another carb. Check all related ignition components. Check for spark next time it dies!!! If you have no spark before it cools then it is definitely ignition related, if you do then it is fuel related.

Do you have points or HEI. If you converted to HEI, maybe the module is bad.

Ok. Thanks Davii. So what's the best way to check for spark? Pull a plug wire and see if a spark arcs from the wire terminal to the engine block, while trying to start the car?

Steve

You can pull a plug wire, stick a screwdriver in the wire boot, hold it close to metal and crank the engine. The best way is to use a Spark Tester. You use it in place of the screwdriver and can get one at almost any parts house. Most of them are adjustable, and as such better. Set it for about 10 KV to begin. If you have points it should go to 29 KV, HEI should come close to 40 KV. These will both be lower during cranking as opposed to running due to reduced battery voltage.

Ken Styer

Vapor Lock ?

Could it be my fuel pump? But what would cause it to pump less gas or stop pumping gas, when the engine is warmed up?

Steve