Over Revving Outdrives

[bjac]

I have twin 350 Mag MPI's with B3 outdrives. Over the last couple of summers on a couple of occasions when I went to power up to go on plane (which I do slowly, not just full throttle from idle) the engines over revved and I went no where. I immediately pulled the throttles back to idle and checked for possible weeds in props etc., my trim tabs and the position of the out drives. All seemed fine. I did go to idle, then to reverse, then back to idle before I slowly increased throttle and then all seemed ok.

It happened again the other day when I went to go on plane. Trim tabs where up all the way, drives where down all the way and over rev. After a couple of times trying, it finally came up on plane without issue and ran that way for a half hour. I''m getting ready to pull for the season and would like some ideas to check for this problem. Any help is appreciated.

 

[Little Ducky]

I had this happen to one of my engines this year.

It was at night so I had to limp it back to my home marina at no higher then 2500 RPM on the port motor.

The next day looked at everything and found where I hit something and then took the boat out my the nearest swim area so I can inspect a little closer. I originally thought I might have spun a prop .... but after inspection and only finding a cracked cavitation plate I took the boat out for a good spin and could not recreate the issue. And since then everything seems to be just fine.

I would think either a spun prop hub requiring a new insert or a broken shaft coupling.

 

[bjac]

I had this happen to one of my engines this year.

It was at night so I had to limp it back to my home marina at no higher then 2500 RPM on the port motor.

The next day looked at everything and found where I hit something and then took the boat out my the nearest swim area so I can inspect a little closer. I originally thought I might have spun a prop .... but after inspection and only finding a cracked cavitation plate I took the boat out for a good spin and could not recreate the issue. And since then everything seems to be just fine.

I would think either a spun prop hub requiring a new insert or a broken shaft coupling.

Thanks, I'll have my mechanic check this out when I haul out next week.

 

[Espos4]

FYI.......As far as I know, Bravo 3’s don’t have prop hubs that could “spin”. The props are solid.

A broken coupling between the upper and lower units would most likely result in no movement of the prop at all.

Maybe a slipping cone clutch??

 

[Little Ducky]

FYI.......As far as I know, Bravo 3’s don’t have prop hubs that could “spin”. The props are solid.

Good to know. But bad for the tranny.

 

[Lazy Daze]

Definitely no hub on B3 props. However, the "coupler" could be starting to flake out. It's a rubber "hub" between the engine and drive... which means... engines have to come out to change it.

If there's nothing physically hanging up on/around the drive and there's no significant damage and drives are being used properly for the conditions...