Probably a 2 part question here. This is a motorhome. First, is the fuel issue. I'm not getting fuel after it's been sitting for 3+ days. It will crank and crank and no start. Dump some gas in the carb and fires right up and runs. Not sure what's happening. My guess is the fuel pump is at fault. The fuel is draining back to the tank and the fuel pump can't prime it when turning over, only when it starts up due to higher rpm. However, there should be fuel left in the bowls of the carburetor so it should start anyway. So, what is the possible issue here, is it one or both of them causing the issue. If it's the pump, since they aren't available, do most go with an electric pump located by the tanks? Trying to get an idea of what's going on. I'm going to remove the hose of the carb and crank it over and see if fuel comes from the hose. That might narrow it down. Also, is replacing the carburetor is an edelbrock 750 a good thing. What are the pros and cons of doing this. Sorry, I don't like Holley, so please don't recommend.

 

If your fuel pump is the camshaft actuated mechanical arm type places like Jeg's or Summit Racing should have decent quality replacements available---plenty of those older engine designs being raced even today.

This sounds like a fuel issue which would tend to be centered at the pump if its original to the engine. Initially I'd agree with your guess about the pump not priming itself.

I don't know I'd go with an in-tank pump as those were used when higher pressure fuel injection began. A frame mounted pumped keyed to the run position of the ignition switch would be my first choice for convenience of installation and future service should that be necessary.

 

Th fuel pumps from summit/jets will not work because of the power steering bracket and pump.

 

Does it have dual tanks, if so, it's the selector switch.

 

If it was the selector switch, then it wouldn't run at all, correct. I don't understand how that switch could keep it from starting. It makes sense if it doesn't run but I have driven it and it runs great and drives great. Plenty of power. If the valve was an issue it would also cause other issues, right? or am I wrong.

 

It is part of a loop, to return fuel, I had a friend that had issues with his, was when the heat under the hood built up, the problem seemed to start, a crack was opening, causing it to suck air, if it is sufficient enough, heat would not be required.

 

If his is like the 1982 E350 Class C RV I had there is no return fuel. It has the actuated mechanical arm type fuel pump mounted on the engine.

The fuel tanks are selected by a solenoid valve on the frame with one wire going to it. The solenoid valve will be either on or off to select the tank the switch on the dash is set to.

Yes my E350 did the same as yours and so does a lot of other 460 RV's of that era. The fuel pump on mine had been changed many times before I got it and changing the fuel pump did not help.

I think the fuel must either evaporate or drain down into the engine while setting for a few days and I do think the fuel pump check valve was at fault.

A after market inline electric low pressure fuel pump (7-12psi) was installed on the frame so the engine could be primed before starting the engine. This seemed to work out well as long as I had the RV. I no longer have the RV as I traded it in for a Class "A" on a F53 chassis.

 

My first guess is the front fuel bowl is leaking fuel, and after sitting a few days all the fuel leaks out. Then, when you go to start it, you have to crank it long enough for the fuel bowl to fill back up before it will start.

Been there, done that.

After it's been sitting for a day feel around the bottom side of the front fuel bowl, particularly around the accelerator pump diaphragm cover, and see if it's wet with gas. If so, I reckon that's your problem.

You say it's a '78 with the original carb? (maybe rebuilt a few times along the way) After all these years I'd say the design has proven itself and today it just needs some routine maintenance. Swapping carbs will be a lot more work that replacing a few gaskets...just saying.

 

If you have a Motorcraft carb, the fuel accelerator pump is on the bottom of the bowl, they leak when they get old, draining the bowl when it sits a few hours.