shmick__shmacky Posted July 16, 2007 Share Posted July 16, 2007 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 Link to comment Share on other sites More sharing options...
Valv Posted July 16, 2007 Share Posted July 16, 2007 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. Link to comment Share on other sites More sharing options...
shmick__shmacky Posted July 16, 2007 Author Share Posted July 16, 2007 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 Link to comment Share on other sites More sharing options...
Valv Posted July 16, 2007 Share Posted July 16, 2007 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. Link to comment Share on other sites More sharing options...
Surface Tension Posted July 17, 2007 Share Posted July 17, 2007 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. Link to comment Share on other sites More sharing options...
Black_Bay Posted July 17, 2007 Share Posted July 17, 2007 If it is dirty carbs like, Surface Tension said, you could run the engine lean and blow the powerhead. Link to comment Share on other sites More sharing options...
shmick__shmacky Posted July 25, 2007 Author Share Posted July 25, 2007 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. Link to comment Share on other sites More sharing options...
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