1999 alumacraft magnum motor adjustment

npauls · #1 11-17-2009, 08:26 PM

I just bought a 99 alumacraft 165 cs magnum boat with a 40 hp merc 4 stroke on the back. I have had it out a couple times and have had a few issues with the way it runs. Now I know this motor is pretty small for the boat but I have been told it should perform alot better then it has so far. I am just wondering if anyone on here knows anything about adjusting the motor at the mounts and which pitch I should possibly have on this boat. right now I just have the stock prop and when I trim up after getting on plane the motor seems to "blow out" where the rpm's go through the roof so I have to back it off until the rpm's go back down to normal. If anyone can tell me what I should do to try and cure this problem it would be greatly appreciated. I would like to adjust some things and get it out on the water and test it out this weekend before the ice hits down here in southern alberta.

thanks,

Nate

jet boater · #2 11-17-2009, 11:46 PM

Sounds like your cavitating. The prop is drawing air along with the water. You need to either move the motor down lower or adjust the angle of the motor.

npauls · #3 11-18-2009, 07:56 PM

I can drop the motor one more set of mount holes. Will this be enough to make a big difference. What would I have to do to change the angle of the motor?

Nate

jet boater · #4 11-18-2009, 09:56 PM

You said that it only happens when you trim it after you get on plane. There is a limit on how much you can trim after on plane. you may be trimming too much. Each boat and motor combination are different so you may just have to try different combinations. As for lowering the motor, when you have the motor completly down and on plane does it cavitate. If it does then you have to drop the motor.

npauls · #5 11-19-2009, 05:48 PM

If I leave the motor trimmer all the way down it won't cavitate but doesnt move very fast at all. The motor will only trim up so far on this boat when going full speed. From what I have found out on the net is that the motor trim is set up so that when maxed out it should be going full speed not blowing out the prop. I think I may try dropping the motor to the last bolt holes and get a stainless steel 10 or 11 pitch prop over winter and see how that works out. I would like a new motor but have to fix and sell my old boat before I will have the money for that.

jet boater · #6 11-19-2009, 08:46 PM

Good luck