[john parks]

I have a 1993 Mariner 135hp 2 Stroke motor. Recently, the motor began to run rough. The number one and three cylinder had fowled plugs. My first thought was the fuel. I installed a water fuel seperator, fuel filter and rebuilt the carbs. The boat ran fine for about an hour and then I could not seem to get the engine to go above 3500/4000 rpms. It ran like it was missing. If I changed the plugs, it would run fine until they fowled. I tested the the switch box and coils. They tested fine. I still changed them anyway. Coils where next. After pulliing the flywheel I found that one of the magnets had come undone. I changed the flywheel and stator while I had it off. Still the same thing. It seems to run at idle fine, but can not get over 3500/4000 rpms and running rough at 3/4 to full throttle. Does anyone have any ideas?

[tashasdaddy]

have you check compression?

[john parks]

120 average across the board

[studlymandingo]

Fouling plugs sounds like either too rich a mixture on those cylinders or an erratic spark. Check all the wires from the switchboxes to the coils and the wires on the coils to ground.

[john parks]

thanks for the idea. This is frustrasting

[Plainsman]

Check all your fuel lines as well for cracks or loose connections.

[AndyL]

I had a bottom seal problem with the same motor. Caused all sorts of erratic behaviour, poor idling and short lifed plugs. Bad starting occassionally and lack of power. Hard thing was getting the powerhead off to fix it as the front long studs were frozen into the exhaust plate. At the age your motor is it may be something worth considering.

[john parks]

thanks, looks like I have some work this weekend