drain the tanks completely.  inspect inside to make sure you dont have any sludge at the bottom. replace your fuel filter/water seperator cartridge and any inline filter u may have between pump and carb (which you should have, it catches the small stuff) and run it. 

do not continue to run on bad gas... 

in the future if its going to sit, either drain the tanks or toss in a bottle of "sta-bil"

I had the same issue with starting when i first bought my boat... one tank had nice fresh gas and the other had gas that sat for over a year and i added about 5 gallons of fresh gas. So when i was at the lake i got low on my fresh gas tank... switched over and no start on the tank with the old gas. So i drained the old gas using a 10$ hand pump from napa . Put fresh gas in the tank and the boat started up but ran like crap. My filter is plugged for sure. So my point is drain the gas and replace the filters that are inline with the fuel line. dont go around the filters.

We use this stuff on the Pontoon boat we leave at the river. It has worked better for us than Sta-bil.


http://mystarbrite.com/startron/

I ad either auto trans fluid or mystery oil (basically same thing) to every tank of gas....at the end of every season I drain fuel tank and run straight trans/mystery through carb with it off boat.