2004 Yamaha 50hp 2-Stroke clutch/shaft Issue?

CornStar

Recruit
Joined
Apr 15, 2019
Messages
2
New to the forum here, a novice when it comes to boat motors. My issue: The boat will move forward at low throttle/rpm, but when I increase throttle to take off, the motor does several abrupt skips & revs way up until it looses bite completely. I have had 4 different props on the boat to test (all good props) and I do not believe it's a spun hub (no damage shown on any prop, marked them too to rule that out). Is there a clutch on these models in the lower unit? Keep reading about a clutch dog...? Almost sounds as if a gear or something is stripped. Or could it be lower unit completely? I would think if it was lower unit, it wouldn't go forward at all. I also do not think it is fuel related, like I said, boat will rev up fine, no sputters ever, go in reverse, & slowly forward is all. Any advice/opinions much appreciated!
 

joeanna

Petty Officer 2nd Class
Joined
Jun 5, 2016
Messages
108
have you checked the LU oil? check for excessive metal fillings/ pieces?
 

CornStar

Recruit
Joined
Apr 15, 2019
Messages
2
Yes, lower unit oil is full & good. I might add, I did replace throttle & shift cables before winter, could the adjustment cause such violent moves from motor IF in case it was trying to slip out of gear? I just don know why it would be a sporadic skip then loose bite @ the top end...
 

joeanna

Petty Officer 2nd Class
Joined
Jun 5, 2016
Messages
108
If it worked good before the cable change, I would assume the cables are out of adjustment. If so I would get them adjusted properly before you do any damage to your LU
 

rejesterd

Petty Officer 2nd Class
Joined
Sep 20, 2018
Messages
142
I would go through the link/sync procedure in the service manual (since you replaced the cables), but if your idle is steady, I don't think that's your problem.

If you're sure you did the marking test correctly and ruled out a spun hub, I would do a compression test. It's possible that the piston rings are worn or you have a leaking head gasket.

If compression checks out, then get a carburetor rebuild kit and clean/rebuild the carbs.
 
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