'75 Mercury 850 slips at higher RPM

[cpad33]

I just bought a boat with a 1975 Mercury 850 (85hp) on her tail and recently it started slipping it seems. At low throttle it runs fine at a low speed of course, but when you throttle up and remove your hand from the lever it starts to speed up. Once it gets to a certain point the boat slows and the RPMs skyrocket. I don't know a lot about motors, but I do like to try to work on things myself. It almost seems like when it tries to get into 2nd gear (if they work like that) that it's not catching. Again, low speed at low RPM is O.K.

 

[Bcmagna]

Re: '75 Mercury 850 slips at higher RPM

I had a 20 hp motor that did that exact same thing,Turned out that the prop was cavitating . the motor was a long shaft and I had it on a short transom so I moved it up 5" and it never missed a beat. I thought at first that the mercury prop has spun but after a new prop and the same problem happened again the guy at the prop shop told me about cavitating . this is when the prop doesn't have enough water to work and its just like you threw it into neutral, and it would work just fine when it slowed down. just a thought bcmagna

 

[Ross J]

Re: '75 Mercury 850 slips at higher RPM

Could be cavitation or the hub is spun. Try another prop and see if the problem goes. <br />Ross