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Outboard will increase rpm boat doesn’t move

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hchiles5

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I’ve got a Yamaha F115 with spun prop like symptoms. The engine will go into gear just fine and revs up fine but the boat doesn’t move like it should. Once you get over 3K rpm it just revs out to over 5k and no more acceleration. I’ve tried 2 props, marked the prop and hub to check for slipping, checked the shift cable for damage, taken the lower unit apart to check clutch and checked the crankshaft splines for damage. All appears to be good, is there something else I can check in the lower unit?

F115TLRD
 
hchiles5 said:
I will also add that this happens in forward and reverse gear. Could the driveshaft be slipping on the pinion gear?
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You would definitely hear something disturbing if this was the case. Find a way to reach the prop, make sure it can't start, put it in gear and try to turn the prop. If it turns and it doesn't sound like anything in the Yamaha is moving, look at the hub- if it's not turning, you have a bad prop.
 
You stated that there was nothing wrong in the gearcase.-----If driveshaft was SLIPPING on the pinion, it would not drive at 3000 RPM.----So in my opinion it should be easy to solve this issue.
 
jimn said:
You would definitely hear something disturbing if this was the case. Find a way to reach the prop, make sure it can't start, put it in gear and try to turn the prop. If it turns and it doesn't sound like anything in the Yamaha is moving, look at the hub- if it's not turning, you have a bad prop.
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I can spin the prop in gear and watch the flywheel move.
 
racerone said:
You stated that there was nothing wrong in the gearcase.-----If driveshaft was SLIPPING on the pinion, it would not drive at 3000 RPM.----So in my opinion it should be easy to solve this issue.
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I stated that I took the lower apart to check the clutch, I didn’t go any further. What else should I check that would be easy?
 
hchiles5 said:
I stated that I took the lower apart to check the clutch, I didn’t go any further. What else should I check that would be easy?
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And this prop has been on the Yamaha since you bought it? When the RPM increases from 3000, do you see signs of cavitation or aeration in the prop wash? If so, what is the pitch of the prop? Can you go faster by advancing the throttle slowly, rather than quickly?
 
Have you recently added a new depth finder or relocated a transducer that could create a slip stream that feeds into propeller area? I've seen that cause this issue. What type of boat do you have this engine mounted to?
 
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