1977 E350 carburetor problems

I have a 77 E350 motorhome with a 460 and am having fuel problems. The carburetor is an Edelbrock 750cfm which is new and I have replaced the tank switching solenoid. My problem is that sometimes it acts as if it us running out of fuel, going up a hill sometimes it will start backfiring, if you let off the throttle it gets a little better. I have replaced the fuel filter as well and checked the fuel pump and it seems fine, no fuel coming out of weep hole. Is this a sign of vapor locking? Please help as I am at wits end with this vehicle . Thanks

Sometimes vacuum advance moving stator wires in distributor can cause intermittent open, when you let off wires move back to close the circuit. Worth a look. Continuity light and vacuum pump required for diagnosis. I see this is old post but might help someone!

Don't know if you found your problem but I have a 78 E350 that was having the same problem. It ended up being the fuel line itself had a hole in it that you couldn't see unless you were running. The lower the gas got the harder it would be for the pump to suck gas and would act like it was running out of fuel.

Or charcoal in a main jet caused by flooding the vapor cannister. We used to put a cotton ball in the hose from cannister to carb. Solved the problem.