OK guys here is my delema. 1991 15hp Johnson, new to me with no history info.
125#compression on both cylinders. When I started it (using drill motor on flywheel nut), no peeing. So at tear-down, the water pump impeller looks like it was a new replacement YEARS ago but installed with no lubricant & sat for a LOOONG time.
It (impeller) was seized to the cup, but was missing 3 vanes.
I tore powerhead off, could not find missing impeller pieces, water tubes clean, sideplate passages like maybe it ran very little as really clean inside. Thermostat was clean.
Rebuilt carb & fuel pump. New fuel line from pump to carb, & using known good fuel tank. Also using it in 50 gallon water tank.
After reassembly, it still not wanting to start by rope, so maybe top crankcase seal bad,
replaced that. But helping at all.
It will start after numerous revolutions using drill motor, BUT only if I loosen throttle
stop at no start in gear stop, loosend it allowing timing plate stop to bypass stop & giving a slightly higher RPM in neutral,
BUT still have to play with choke at about 3/4 closed, anything lower than 2600 RPM it will die or if choke is backed off. OH YES, this is also with a different rebuilt card.
The only thing I have not looked at is inspect the reed valves. I made a adapter plate to bolt onto carb/manifold studs & installed a vacuum gauge. Now with numerous revs with drill motor, all it gets is 6″, which bleeds off in 6 seconds.
I am new to this testing, so what am I seeing? Is the reading normal? But more
important, should this bleed off that fast? Suspect reed valves are the culprit. ??
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