CF6873

On Sunday I ran the 68 in an Autocross. The car ran strong in the first run. A little hard to start 10 minutes later and when it did start a big puff of black smoke. About 30 seconds into the run there was a long straight and when I nailed second gear the engine just died. As I let off of WOT it slowly came back on and it idled rough for a few seconds after the run was over. In the afternoon session the exact same senario. Strong first run and a dieing engine for the next two runs. When I pulled the air cleaner off I could see scorched paint where the exhaust feeds into the intake and in front of the carb mount where the exhaust circulates under the front of the carb.
It seems to me that the fuel is boiling in the carb and causing the shut down. A mechanic friend told me about tapping and plugging the exhaust passage holes just under the carb to not let the exhaust reach the carb. I am going to give that a try. I do not have a return line to the tank and my pump to carb line is not touching the block anywhere. Any input from you guys with similar experiences would be welcomed. Thanks, Craig :cheers:

Gary79

having experienced fuel pump failure and vapor lock. i would say check your fuel pump. anytime i have had vapor lock the engine stumbles and dies and doesn't restart or stay running. sometimes a good 15 minute wait, before re-starting. fortunately, i have never had either problem with my 79 vette, had fuel pump failure on my 69 GMC pick-up, and vapor lock on my 78 Chevy van.

Matt Gruber

i'd tape a fuel pump gauge to the windshield and verify pressure first.

70vert

Been there/done that
THE FIX = phenolic block between the carb and intake. Gut the butterfly out of the exhaust bypass valve (I really don't know what else to call it) that sends exhaust gas to the intake when cold.

1LE

Could also be a fuel filter.

marshrat99

:iagree: definitely pump or filter or water. :cheers:

CF6873

Why would a fuel filter be temperature sensitive? It only does it when it's hot.
The heat riser is removed from the exhaust. The spacer plate sounds like a plan. Thanks Guys. Craig

PRNDL

I had very similar symptoms at the dragstrip. Somewhere around 5000 rpm the eingine would just quit - almost felt like a rev limiter was hit - I would get off the gas, but engine was still running and I could proceed, ie floor it again and engine would recover and pull ok. I produced some high 15 second timeslips this way. My fuel return line is not in use. I replaced my part rubber pump to carb fuel line using a very large inline filter and no more problems. So, in my case the problem was apparently fuel delivery, and somewhere in the fuel line it was either constrained or gas was heating up.

Matt Gruber

GM learned to use a return line as in my 72.
i added it to my 61 :cool: