1983 Evinrude 90hp felt like I hit something, but I didn't. What is it?

[shallow hull]

OK, had the family out tubing today. Everything went fine, engine ran great. After about an hour or more of dragging them on the tube around the lake, we were going along and all of a sudden, a "thump". It felt like we hit a big catfish or something with the motor. About 20 minutes later it did it again. Engine still running good, no signs of hitting anything. The water was not shallow.

Any ideas of what it could be? Something I need to worry about/get fixed?

Thanks!

 

[Tim Frank]

The intermittent stuff is the hardest to diagnose.
Sounding like a worn clutch dog.
If so, it will get more frequent.

 

[miketheknife]

Any idea what RPM when it happened. Sometimes a temperature problem or a bad temperature switch can limit the RPM and the motor will jump. Could also be a power pack problem. Just went through this. Was a bad switch.
Mike

 

[shallow hull]

Not sure of the RPMs, probably running 2/3 to 3/4 throttle. Pretty weird, felt like real solid thump

 

[willamettejeff]

Check also for prop hub slip. Next time you go out, mark a line across the prop housing and the hub. If you get the bump again, check that the line you made is still aligned.

 

[emdsapmgr]

Follow up on post #2. A worn clutch dog or a shift adjustment that is incorrect will cause this. Not a cheap fix-if that's it.