I just bought a 6sh 1987. It ran ok, I took it out and progressively throttled up until I was full on. At one point it lost power and just stalled. From then on, it would start but as soon as I would put it in gear it would stall again.
So I did:
new, good fuel. Verified it goes all the way to the fuel pump no restriction.
open the carb (was already super clean)
changed all carb gaskets, float, needle pin
no obstruction in any jets
Changed the gaskets and diaphragms in the fuel pump.
No difference, it does the same again. Took it to a buddy of mine, an engineer on a huge tug. We pulled the plugs after cranking it many times: dry. Dumped some fuel in the cylinders: fired right up and then stalled. His conclusion: fuel delivery problem. We dismantled the carb again, he blew in it upside down, no flow at all. Blew at it right side up, air flowed but with restriction. He says the problem is somewhere there.
Here's my take on it. The fuel pump is pretty simple. Can't be any diaphragms because the motor acts the same with new ones as it did with old ones. The only things left are the check valves in the pump but they didn't look bad at all and neither was jammed.
Any clue, anybody?
So I did:
new, good fuel. Verified it goes all the way to the fuel pump no restriction.
open the carb (was already super clean)
changed all carb gaskets, float, needle pin
no obstruction in any jets
Changed the gaskets and diaphragms in the fuel pump.
No difference, it does the same again. Took it to a buddy of mine, an engineer on a huge tug. We pulled the plugs after cranking it many times: dry. Dumped some fuel in the cylinders: fired right up and then stalled. His conclusion: fuel delivery problem. We dismantled the carb again, he blew in it upside down, no flow at all. Blew at it right side up, air flowed but with restriction. He says the problem is somewhere there.
Here's my take on it. The fuel pump is pretty simple. Can't be any diaphragms because the motor acts the same with new ones as it did with old ones. The only things left are the check valves in the pump but they didn't look bad at all and neither was jammed.
Any clue, anybody?