But
then I noticed a ringing rattle under the cover, and found the flywheel nut
loose; I could remove it with my fingers.

Obviously you have people working on your engine that know very little of its
technical aspects, and are costing you money.

The loose flywheel nut will cause the flywheel key to shear which would throw
the engine out of time. Remove the flywheel and check that key. If sheared,
you'll no doubt need to clean up the crankshaft and flywheel tapers, install a
new key, then torque the flywheel nut to exactly 105 foot pounds. Any less
torque.... the key will absolutely shear!

The rectifier is not under the flywheel. It would be on the starboard side of
the engine. It's a barrel shaped dome about 1" high with a triangular shaped
base which is attached to a bracket with two small different size bolts. It
will have three (3) wires, a Red wire, Yellow wire, and a yellow/gray wire
(some do not have the yellow/gray wire but rather have two (2) yellow wires).

Bogging out when throttle is applied is usually caused by one (or both) of two
things. Clogged carburetors or a sticking timer base under the flywheel when
throttle is applied. Even if the carbs were cleaned by your present
"mechanics", from what you've said, I wouldn't have any faith in their
rebuilding capabilities.

The timer base sticking..... with the engine NOT running, spin the prop and put
the engine into forward gear. Have someone else slowly apply the throttle up to
full throttle while you watch the timer base. It should smoothly advance up to
the black rubber stop cap on the end of the full spark advance stop screw.

NOTE.... Visit www.maxrules.com which is the MasterTech website. Go to the
Evinrude/Johnson forum to list your problems. Be sure to list the model number
of your engine when you do so that we can determine exactly what engine you
have.

Joe Reeves (30+ Years With OMC)