Motor Problem

[shmick__shmacky]

I ran the boat on Saturday, when i was running about 4500 RPM's it would surge to about 4700 RPM's real quick and then back to 4500. It would happen about every 2 minutes while running. It would do it 5 to 10 times and then quit for a while and then do it agian. It seemed to only surge like that at around 4500 RPM's. Other than that it was running great even during the surges. It is a 90 hp 1999 2 stroke Johnson. Any thoughts on the problem would be great.

Thanks

[Valv]

Was it trimmed properly and not too high ? 4500rpm or 4700rpm at WOT are too low, actually 1000rpm too low, you must have a prop with too high pitch or other problem.

[shmick__shmacky]

I wasn't trimmed up to much and wasn't running WOT, WOT I am at 5500 RPM's. Others have suggested a spun hub. Just looking for all thoughts so I have several options to look at when I trouble shoot the fix.

Thanks

[Valv]

Definitely not a spun hub, you would have noticed it when taking off or when a lot of torque/power is applied, not during regular traveling.

Being a Johnson yours should be a carbed motor, correct ? Then it could be a dirty carburator jet, or a faulty plug, etc.

[Surface Tension]

It might be a plug cutting in and out.

It could also be a dirty carb and that would worry me. Replace the plugs and fuel filter and do a total gas line check including the bulb. If that dosen't fix the problem its time to clean and rebuild the carbs and fuel pump. I wouldn't use it till thats done.

[Black_Bay]

If it is dirty carbs like, Surface Tension said, you could run the engine lean and blow the powerhead.

[shmick__shmacky]

If it is a spark plug cutting out or a clogged carb, those problems would make the RPM's jump up and not down?

Thanks for all the reply's, I will be at the cabin and checking it out this weekend.