If that surge is a slow gradual up/down surge, that would be a fuel problem. If a instantaneous sudden up/down surge, that would be a ignition problem. Which does it appear to be?

*You're saying that the engine actually obtains and holds the full throttle setting for at least 5 to 10 minutes. If this is correct, that eliminates the carburetors as they do not come and go... once they're faulty, they stay that way.

*Also a possible fuel restriction is out of the question as you've changed tanks/fuel.

*And you've went the pumping the fuel primer bulb route, acting as a manual fuel pump... so that eliminates a fuel pump problem.

Ignition?.... Remove the black/yellow wire from the ignition switch temporarily (kill circuit). If that cures the problem, replace the ignition switch. Make sure that the lanyard kill switch is either disconnected or not interfering. If no change..............

Closely inspect visually the stator under the flywheel. Should there be a sticky looking substance dripping from it down upon the powerhead area, replace it as that indicates it is encountering a meltdown scenario that results in a AC voltage drop to the powerpack's capacitor.... weak, erratic, and eventually no ignition when it heats up.

Question.... Has the tachometer been acting erratic lately?

Let us know what you find.

thanks for the reply Joe - great ideas. I am out of town for another week or so but will get to it when I return. Tach has never worked properly

That (above) problem is normally caused by a faulty water cooled voltage regulator/rectifier a$$embly. If your engine is so equipped, both the tachometer and the charging unit can be checked at the same time as follows.

(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

However.... those water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

NOTE: For the later models that DO NOT incorporate a wiring terminal strip, splicing into the "Yellow Wire" mentioned will be necessary.

Normally the Gray wire leading from the tachometer is attached at the terminal strip to another Gray wire which leads from the water cooled voltage regulator/rectifier...... remove the gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.

Solved!!!! Seaweed plugging the thermostat and engine going into limp mode. THANKS FOR ALL YOUR HELP!!!!!!

Right on- thermostat was clogged with seaweed and would go into limp mode. New T-stat and all is good (for now) THANKS!!