intermitant loss of power at wot

[ronreed]

I have a 93 force 120 that will not run over 3000 rpm, then suddenly it will run fine. Shut it off and it will run 3000 rpm at wot. Changed fuel lines, filter, primer bulb, fuel pump, and cleaned and even replaced carb. Idles fine runs fine up to 3000 rpm then it may or may not run wot.

 

[SkiDad]

have you checked the vent on your fuel tank ? Have you tried a portable gas tank ?

 

[ronreed]

built in 20 gal fuel tank, checked the vent, the only thing I have not tried is a portable tank. You can be running along at 3000 rpm then it might suddenly start running properly.

 

[SkiDad]

another dumb question, but you wouldn't happen to have a closed hub prop running on a dual exhaust lower unit ??

 

[ronreed]

No its the proper prop, I pulled the fuel pickup today and replaced that, and I discovered the new primer bulb was not working properly, so I replaced that. I am running out of ideas. It makes no sense, It struggles pulling 3000 rpm then all of a sudden it will run 5200 as long as I don't shut it off. Then it may or may not run over 3000.

 

[jerryjerry05]

That sounds like the stator is failing??
​They used 2 different ignition systems on your motor.
The older, Prestolite and Mercury's ignition.
Do a spark and compression test.
It sounds like the comp is ok. But you never know.

They used 2 different fuel pumps too.
Make sure the valves in the old style are working.

Older: check the trigger wires and see if one isn't loose under the shrink wrap???

outboardignitiondotcom has test procedures for your motor.

 

[ronreed]

switched fuel pump to square type, I have a 97 120 force that lost a cylinder , will that ignition system transfer to the 93 block

 

[Jiggz]

Personally, I'll check on the carb throttles first to make sure the linkage is not lose. Next will be to use an external tank. These two tests are practical and costs less not to mention easy to do. If you have not installed a clear fuel filter between the fuel pump outlet and the carbs inlet, I highly recommend it. This will be very helpful in troubleshooting fuel related problems and yes it costs less than $5 (Fram G2, even comes with hose clamps). It's more for troubleshooting than filtering.

 

[jerryjerry05]

What ignition is on your motor now?
​They used 2 kinds.
The 97 probably won't work because of the flywheel.

 

[ronreed]

It has the Mercury ignition, gonna try the portable fuel tank idea , great compression 150# per cyl. . Ive seen coils get hot and quit, but this problem comes and goes . It might be running terrible 3000 rpm max. then all of a sudden it takes off and runs great., till you shut it off then its back to 3000 rpm . It might not run wot all day. It never runs the same twice, very frustrating .

 

[roscoe]

This sure sounds like ignition.
Not getting spark on one cylinder, then you do, and it takes off.

Could be loose/broken wire from stator, stator itself, trigger.
Coils usually fail as they get hotter.
Switchbox usually fails and is done.

Check all other wires for tight connections, loose or broken insulation.