Hello Taber Alta. Bought a brandy new Suzy WaterBuffalo there in 75, on my way through.
Anyway, I think you have one of three problems.
1) the pump is sucking air, or
2) the diaphragm return spring inside the pump is not working,or
3) the delivery line is restricted
There are easy tests for this..... Start with a full fuel bowl in the carb. Then you will need to perform a fuel volume test. This involves rerouting the output from the pump into a clear glass container of at least one quart capacity. More is better cuz it is less likely to tip over.Then start your engine and observe the fuel delivery. It should be free of bubbles and deliver a pint in about 15 to 30 seconds. The engine should run 2 or 3 minutes on a full bowl. I refill them on most carbs, through the vent stack with a tiny funnel.
-Bubbles means its sucking air. Go find the entry point. Its usually the little jumper hose right off the tank. Often loose clamps. Or a plastic fuel filter on the intake side. The filter should not be on the intake side.
-Lack of output. Could be a restricted supply hose. Could be a failed return spring. Could be a bad or plugged pump.
So remove the fillercap and the supply line from the pump, and observe the siphoning of the fuel into the glass container. If no fuel comes or it seems weak, blow out the line back to the tank with compressed air.Dont go crazy with air delivery. Have someone listen at the tank for bubbling.Tell him not to breath in the fumes;they're hard on the brain.Rubber lines like to rot from the inside, out. If yours are old, replace them to be sure.Next, remove the pump and check the return spring. Clamp the mounting flange in a benchvise, in its normal working attitude, to immobilize the pump. Grab the pump arm and pump it down,then release it. It should pop back up on its own. It should not be flopping around. And you should hear the check valves inside making nice check-valve noises. If you plumb a pressure gauge to the output side, it will read air pressure after 3 or 4 strokes. A good pump will make 4 to 7/8 psi.
-These tests should be performed in the order that they are given, and you can quit at whatever point you discover the problem.
- Now if everything checks out OK and you haven't found the problem, you will need to pull the sending unit out of the tank and pressure test it and check the filter sock.
-Well there is one other possibility; a failed eccentric on the front of the cam. So, when you remove the pump for testing, shine a lite in there. Make sure it's securely attached and in good shape.
-Somewhere here lies your problem, I'm pretty sure.Good luck.
Oops theres one more possibility. You're fillercap is not venting. But a good pump will collapse the tank before finally quitting.Check it anyway.
Good hunting.................Since you say the line is delivering fuel ok, perhaps you could start by the removal and testing of the pump. But I must tell you that just because the fuel runs out of the hose, or that you can suck fuel out of it, does not preclude that the pump wont suck air. So if you jump to the pump test and eccentric inspection, and cannot find the problem; then I would recommend that you back up the bus to square one.
