Chances are you need to have the carbs rebuilt.
However, it could be several other things.
Best to take it to a local shop and have it checked out.
As for the year - give us the model # on the engine (sticker on the
passenger side beside the motor mount bolt).
Who did you buy this boat from and did you not take it for a test drive to
verify it ran properly? Also, did you not get the year from the owner.
Should have been on the tag receipt or the title if your state has titles.
--
Tony
my boats at
http://t.thomas.home.mchsi.com
"Andy" wrote in message
om...
Well this is my first post to the group and hopefully its not to far
off topic but I have a few questions.
I have been around boats all my life and finally just bought my own 
Its a 20 foot Sylvan pontoon with a 40hp Johnson Tracker on it. The
boat is a 1991 but I dont know where to start to find the date of this
motor, any help on where to look would be appreciated.
My other question is with a motor problem. Right now when I give it
full throttle it will bog down, then speed up and back down again,
then sometimes almost or will die. At lower speeds it seems ok and
idle its perfect no hiccups.
The guy at the local marina said it sounded like maybe a clogged fuel
line or tank so he gave me another one to test out. I put the new tank
on, with a new tank of gas and it still did the same thing.
Any help on where to start would be greatly appreciated.