86 marathon fuel pump pressure

[rdmcavo]

Does anyone know what the pressure should be at the output of the fuel pump on a 1986 EZGO 2 stroke ? Mine measures about 1/2 pound, maybe a little less and I think it should be in the 2 - 4 lb. range.

thanks Mc

[dougmcp]

I think the fuel pump creates it's pressure from the crankcase, if your compression is low, the fuel pump pressure will also be low.
What kind of problems are you having and have you done a compression check?

[Michael Eddie]

If your seals are going, it will reduce crank case pressure as well. Is it not running right now? If it starts but runs choppy, try spraying the seals with starting fluid, does it run better?

[rdmcavo]

I did a rebuild kit about 4 weeks ago. New cylinder, piston, rings, bearings, seals, crank, rod, etc. It ran fine for about 2 weeks then acted like it ran out of gas with about 1 to 1-1/2 gal. of gas in the tank. I added one gal of gas and had to prime the fuel pump to get it going again. It did fine for about a week and then acted like it ran out of gas again. This time it had 3/4 tank of gas. I primed the fuel pump again and shot some gas into the carb to get it started. It ran for a few minutes and quit again. I removed the carb and the bowl was empty with the inlet needle valve stuck in the closed position. I cleaned the needle valve and the orifice (more on this later) reassembled the carb. and the bowel filled one tine (no priming necessary) but when that bowl of gas ran out it quit again. I assume the valve got stuck again. I removed the gas line from the tank and shot a short blast of air in the line which seemed to unstick the valve because the pump started pumping gas again ( I could see it flowing through the gas filter but a really weak stream). So I disconnected the line from the fuel pump to the carb and put a pressure gauge on it. As I cranked the motor got about 1/2 pound or a little less pressure. I disassembled the pump and it looked very clean inside but I noticed a small crease in one of the mylar? valves. The crease ran from the center hole where the rubber holder goes through the disk to the outside edge of the disk. I tried to flatten the disk as best I could and reassembled the fuel pump. It still puts out a little less than a half pound of pressure. I ordered a new pump but it will take a week or so to get here.
Now about that needle valve. On all of the small engines I have worked on the needle has been made of brass and has been attached to the float loosely with a fine wire so that when the float went down it pulled the needle down away from the orifice. This carb has an aluminum needle and it is not attached to the float. The valve must open by its own weight or the fuel pressure. Aluminum is about 1/3 the density of brass (thus weighs 1/3 the weight of the same size brass needle). That's why I wanted to know what the fuel pressure should be from the fuel pump.

Mc

[Michael Eddie]

The valve must open by its own weight or the fuel pressure. Aluminum is about 1/3 the density of brass (thus weighs 1/3 the weight of the same size brass needle). That's why I wanted to know what the fuel pressure should be from the fuel pump.

Mc

Unfortunately the fuel pump pressure does not have anything to do with the carburetor. The float just allows fuel into the carburetor, it does not do anything about getting the fuel to it. It is crank case pressure that makes the fuel pump work.

Either the hose coming from the crank case is bad or leaking, piston rings are bad, or the seals are bad. Did you damage the seals when installing everything back? What kind of compression are you running now? Check the fuel lines for cracks or holes, and check the fuel pump diaphram for punctures.