Bad reed valves on 1991 15hp ?

[LeeRoy Wisner]

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. ??

[fleetwin]

Well, will try to address this, you have mentioned many issues.  Once you get the engine started, does it seem to run normally (on both cylinders) at the higher RPMs it will run at?  If so, this makes reed valve issues less likely.

Are you sure you cleaned that carb completely?  These carburetors (with the plastic bowl) were noted for problems with the rubber low speed pick up hose that feeds from the plastic main fuel pick up to the brass tube leading to the low speed circuit in the carb.  There is still a chance that even if that hose has been replaced, left over debris from the old crumbling hose has clogged the pick up tube/circuit.

The plastic tops on these carbs are another source of trouble, easily cracked/deformed gaskets, expensive to replace.  So, my money is on the carb being messed up.  Does the fuel pump work OK?  Sometimes, a broken diaphragm can cause fuel to leak directly into the cylinder port and flood one cylinder at low speeds.  But, if this was the cause, usually the fuel pump would be inop as well.

As for your vacuum tests, OMC never published any sort to tests like this for their engines.  I’m guessing they felt the results might vary too much and create more confusion than help.  Chances are good, that you wouldn’t see any vacuum reading at all if one of the reeds was broken/stuck open.

I’m pretty sure you can sneak that intake manifold off there to inspect the reeds without too much fuss, even though the lower pan kind of hides a few of the bolts, the rewind will have to come off as well.  Be sure to order the correct intake gaskets and don’t mix them up.  Do not use sealer on intake gaskets.

You never found the left over pieces of the impeller?  Did you inspect the upper water tube grommets?  These engines are known for constricted upper water tube grommets caused by salt build up when used in salt water.

Finally, I do not recommend using a drill motor to start/crank this engine.  You could end up over torquing, or inadvertently loosening the flywheel nut, which may lead to a sheared flywheel key or distorted flywheel/crankshaft tapers.

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