I've had this problem with my Roadrunner when it had a 383 and now with a hemi. I would have to crank the engine for a very long time before it would start. I put a small electric fuel pump next to the tank and use it only to prime the carbs. It works like a charm. I then outsmarted myself, I added a vapor separator and 1/4" return line to look like a hemi setup. The electric pump only had enough pressure to run the fuel back to the tank through the return line. Pinched off the return line and now it works fine again. Don't forget you need a low pressure electic pump or you will blow out the carb seals.