i have a 68 ss 396. it shuts off when running in park after a half hour or when driving it. then it is hard to start. when it does start it will run for a second then shut off or it will run until you tap the gas the in will shut off again. i have a msd 6al ignition box with gutted hei distributor and msd blaster 2 coil. i just rebuilt the dist. with a new pickup since thats all thats in there. i tried a new msd 6al box, and a new coil, the problem is still there. to me it sounds like a ignition problem but now i think it might be fuel because to start it after it dies i have to floor the pedal like it's flooded. someone please help. thanks, joe

could be a vapor lock problem

sounds like a fuel problem to me , when it shuts off take the air cleaner off and check for the accelerator pump squirt i'm betting it is dry. and since it takes a while of running i would check the tank vent or just take tne cap off and see if it starts right back up and if that doesn't help then 496sds might be right, check the routing of your fuel line, does it get near the headers or exhaust ? if so wrap it with some heat tape. had this happen on a73 olds cutlass and it turned out there was rust in the tank and it would run for a while then the pickup would get plugged. after it sat the rust fell away from the pickup and it would run for awhile again. to check for this just use a hose strait off the pump into a fresh can of gas.

I'm thinking pinhole in fuel pump diaphram.