Help Troubleshooting Fuel Delivery

I'm not getting fuel up to the carb, but I am getting fuel to the base of the inline filter between the carb and mechanical fuel pump. The filter does not fill though and I have bubbles in the fuel as the motor is cranking. This is in my 71 with 225 v6. It has a new Holley 390 on it, new mechanical fuel pump, and the sender and tank look new, but I don't have their history. There is no filter on the sending unit. I'm in the process of replacing all the nylon lines and fuel hose in the system. The tank is currently out of the jeep and I've been trying to get it fired from the tank with the fuel out and return lines hooked to it before putting the tank back in the frame. Any thoughts on why I'm not getting pressure to the carb? The fuel fill and vent are just wrapped with duct tape at the moment to keep anything from dropping in the tank, not sure if that is enough to prevent the system from building pressure though.

 

With the output from the pump disconnected, it should spurt fuel a foot out of the line. If it doesn't, there is either a blockage, a suction leak, a bad pump, or a worn fuel pump eccentric.

 

Vented cap, pulling vacuum? Needle valves in carb stuck in the seats?

 

Not implying this is your whole issue but either the fuel filler neck or vent must be open. As the pump sucks gas out, air must replace the volume in the tank that the fuel previously occupied. Without a vent, eventually the pump pulls a vacuum inside the tank. No bueno.

 

Bubbles in the filter sound like an air leak somewhere in the line.

 

x2

 

That's what I was thinking. I've got new nylon tubing now and I'm going to pickup some new rubber fuel hose this week. I'll replace everything and put the tank back in the frame. I guess if new hose doesn't do the trick I'll be pulling the pump and timing cover to check the eccentric...

 

Try feeding from a gas can or similar first and see if any change. That will tell if there is a problem with the fuel tank and feed. A fuel pressure and volume test from there before going any further. If you need I have a fuel pressure gauge you can borrow.

 

Ayuh,..... A crack in the tank's dip-tube,..??

 

Do what nick sez first then realize that a small leak in the fuel pump diaphragm will cause bubbles in the fuel to the filter as well. Good luck.

 

Ayuh,..... A tiny leak, Anywhere on the vacuum side will show as bubbles,.....

 

As Scoutpilot reccommends, for example, double clamps anywhere the rubber hose joins metal tubes, if not a threaded fitting.

I worked on this situation over much of the weekend, on a 1937 firetruck, and found one air leak after another - on the NEW parts, such as the fuel pump filter bowl, and flex-line fittings.