9.9 would probably be the biggest thing you would want to use on it. I have a 6 on my 12 footer, but a 9.9 would be fine.

BTW: Welcome to the BOC from sunny South Carolina! LOTS of great folks and info here!
BB in SC

 

Depends on how heavy the boat is. If it is just a standard jon boat then I think a 9.9 hp motor is as big a motor as I would put on it. Too much power can cause more harm than good.

 

http://www.catfish1.com/forums/showthread.php?t=38918

Just get out your calculator. lOL

 

200 hp. Hold on Sparky.

 

i had a 15 ft. jon and had a 15 hp. on it, it was rated for 25 hp. max, the 15 was fine for the river but i wish i had the 25 on it for bigger water, you'll want to check the weight sticker if it has one, 2 strokes are lighter and smaller than 4 strokes so ya cant always go by the hp. rating