1986 Mercury 9.9 - Increase power/Re-prop

[TheSeaPickle]

A few months ago I picked up a 1986 Tracker TX17 with a 9.9 merc 2 stroke. The previous owner did say the boat would just barely get on plane for him when he drove it, but judging by the registration sticker on the boat it had likely sat for 2-3 years. I put fresh fuel in it and it fired first crank when I tested it in a bucket of water and held idle great with no hiccups.

Yesterday I took it on the water for the first time to test but it would not plane out and reached a max speed of ~7mph at ~4200 rpm. I did add a trolling motor/battery to the front, but I had no other gear other then some life jackets and still had the front deck removed from work I was doing to it, so I don't think it was additional weight that was slowing it down.

I was thinking of starting by rebuilding the carb but I wanted to see about possibly swapping to a 15hp carb instead to increase the power output a bit. I researched a bit and saw a few threads mentioning that the only difference between the 2 engines would be the carb and swapping would essentially convert the 9.9 to a 15, but I also did see someone mention that was only possible on the later 2 strokes and not the early ones like mine. If I can't swap the carb, would there be something else I can do to get a little more out of this engine.

Otherwise would anybody have some insight on what prop I should get? Currently it has a 9" 9 pitch prop which would have been the stock size and is a little beat up. The other 2 sizes that I saw mentioned in the manual were either a 9" 8 pitch or a 9 1/4" 7 pitch but not sure which to go with

 

[flyingscott]

Putting a 15 hp carb on that motor will do you no good whatsoever. Your motor is to early for that the power you have is all you are ever gonna have. Is it running on both cylinders? Have you checked compression? changed water pump? If the motor sat was it stored properly? Maybe needs a carb cleaning.