90hp 2-stroke Yamaha, loss of power after 15 sec. on 3/4 throttle

[Muriel-lake]

OK, that seems like a good idea.., I'll try it.
thanks...

[Muriel-lake]

Did the cover off and looked for exhaust..., NONE.

took it for additional test drive and now the motor is slowing down with the cover off, just like it had with the cover on...

the motor seems to be running rougher at all times.

another fellow, said, "sounds like a Head gasket"
anyone...?

[robert graham]

O.K., maybe not the exhaust leak....have you checked the fuel tank/system for proper venting?...if the tank's vent can't breath it will cause a slow down like you describe....

[Muriel-lake]

That was the 1st thing we checked, even tried a different external tank (new) and new hose., went through the whole fuel system checking lines and filter.

[99yam40]

You can take fuel pump off, take it apart and inspect the diaphragm for hole/tear.

Have read about unbolting the pump leaving hoses on and then pump the primer bulb to see if fuel comes out pulse port to look for leaking diaphragm

[Muriel-lake]

I bought a new Fuel pump and installed it..., took it for a test run..,
Same result. still after 10-15 seconds, once in full throttle, then slows down and runs rough until it recovers in neutral.

does anyone know the next step in curing this...?

taking to another fellow..,
he said, it could be electrical problem, stemming from the coil....? anyone an expert on this..?

Thank you.