I have a 20 hp go devil long tail its a fairly old motor and im only getting 16 out of it with me and one other guy on a 14 foot flat. What are up grades i can do other then boring it out.

Head Work, Exhaust, and Carb. Not sure how much more you will get out of that engine though.... Maybe another MPH or so... The Mods will most likely help you with a load rather than increase your speed.

Thanks uncle j right now with me and my dad about 450 pounds worth of us we can drive over just about anything and when ever it starts to bog down its as simple as just shoving the shaft deeper in the mud and off we go again just now starting to get the hang of running and it sure feels nice having my own boat now

yeah the mods will definitly help you out on the load carrying side, as far as speed like said above you may get a couple out of it, but the 20 is a good motor, happy hunting.