2006 yamaha 15 hp 4 stroke carb problem?

[wings35]

i need help, i have a 06 15 hp , i bought it to use for a kicker on my 248 wellcraft.
bought it from a dealer in march, we installed a trollmaster to control the trottle because of this problem, so the problem was there before we installed it. what it does is
when trolling at say 2.0 or 2.2 for a bit and you want to speed up, i speed it up a number or 2 and get 2.3 or 2.4 things will be good for a1/2 hour or a second and then the motor will speed up on its own.it will speed up to almost 3.2 - 3.5. i have turn it back down a ways then speed back up to 2.3 and then troll a bit ,then it will do it all over again. you can hear it when it is going to do it,it will have a very light stumble then rev up. the trottle linkage does not move when this happens .the dealer told me he cant help me,we changed props,fuel,plugs . i am pulling the cab off tonite to see if something is in it.any help would be great thanks.