Suzuki DF 90

[dalealan]

At 84 hours since new, began running very bad, made it back to the ramp okay, would run okay for a bit then lose power and came in a little over idle. Couldn't find anything obvious. Loaded up came home.
Took cowling off nothing obvious, pulled plugs. Number 3 plug was black and other three plugs were white as new. Put a new set of NGK DCPR6E, put it on the flusher and could not detect any missing or
roughness at all. Couple of weeks went fishing again, boat ran perfect. Fast forward to 164 hours couple of weeks ago, left the ramp and noticed it running badly again for a little bit then smoothing out and running good for a few minutes then surging and max rpm was a little over 3000 rpm. I decided to fish anyway, it would get on top in the flats and then go to surging and losing power again. This time I had a set of the same plugs and the tools so I tilted the motor up and pulled the plugs. This time the number two plug was black and the other others were white. Put the new set in recowled and it ran like new . Caught our 6 reds
and came home.
So I am concerned about the NGK's. They are the factory plug. Is anyone else having any problem with them. Anyone else using a different brand. It is obviously a problem with the plug and not the cylinders or the ignition. I guess I can get a new set and just replace them one at a time. Not the way I do things but I may have to. I don't have a boat dealer and do my own work if at all possible.
Dale

[Moonlighter]

NGK plugs are fine, all I have ever used in mine.

I would be more concerned about fuel….

Was the fuel fresh and clean?

Do you have a water separating inline filter between tank and engine? If you do, have you checked it?

Other thing is battery. These engines demand really good power supply or they will do strange things and what you described is not beyond possible for that.

So make sure the battery is fully charged and in good condition. Remove the leads and clean and replace, tight.

The other thing could be a bad coil….

If you can get your dealer to hook it up to the SDS computer they can test it for that.

[redlowrey]

If the plug wasn’t firing it would be wet with fuel and black, if it was black and sooty it would be more like an injector sticking.
If the plug was sooty the spark will track along the porcelain and not jump the gap to ground.