I've looked over most of the posts on this type of problem and was hoping to find more troubleshooting information. I'm new to boating, so my experience is limited.<br /><br />I've got a '78 20' cuddy cabin with an 898 drive and a 5.7l engine with vortex prop/XHS hub. This setup has been running fine all summer, but occasionally the motor would seem to briefly increase the RPM's with no increase in speed. On my last outing, while cruising on a plane, the engine revved way up and the boat slowed way down. I managed to get it 5 miles back to the launch ramp at about 2000rpm/9mph.<br /><br />I took the hub insert out of the prop and saw no signs of spinning. There was no burnt rubber smell and the engine temp was normal. With the drive in forward, I can move the prop by hand, but it takes quite a bit of effort (takes most of my strength).<br /><br />Most of the posts I've followed on this topic point to the coupler as the likely culprit, but since I didn't smell any burnt rubber and the temperature didn't rise, so I'm not sure. Could this be caused by the forward/reverse clutch in the lower unit slipping? Could this be diagnosed by removing the top cover of the upper unit and watching the vertical and horizontal shafts while rotating the prop by hand? How much torque does it take to rotate the prop in gear?<br /><br />The lower unit has been welded in a couple of places and there is a big chunk of the anti-cavitaion plate missing, so I'm thinking of getting a new unit off eBay. I'm just trying to make sure that spending that kind of money actually fixes the problem and is the best way to get a few more years of use out of this boat. The engine is a '96 crate motor with only 200 hours on it and the boat is in pretty good shape otherwise.<br /><br />Thanks for any suggestions!
