Having a problem stalling going up steep hills. Engine is a 231 with a holley 4 barrel carb. Has electric fuel pump as well. When I get it down to a level area, there is fuel in the clear filter, and gas is being pumped into the carb. Engine will turn over but not fire. Recently, I closed the butterfly all the way and turned it over. It almost fired, so I left the butterfly half open and it started up. Should I be looking at a sticking float in the carb, fuel pressure issue, or something else?