I think its a well known problem with the suzi 2.5hp 4 stroke Kaman... I learned to live with it.. it just doesn't like fast acceleration from idle. It never lets me down once above that critical idle point.. which has to be passed slowly. It alweays starts first pull too..even after stalling if going to fast past that "flat point"
I heard rumours that there is a new carb with bigger jets on the later models but cant confirm. The dealer I got mine from said it was due to the strict emissions controls that these small engines have to comply with ?
Plenty discussions on the problem on the net.. example
DF 2.5 questions - Page 4 - Suzuki Outboard Forum
Please post back if you find a solution that fixes yours..I was a bit reluctant to try the bigger jet size in case no improvement. My Suzi 2.5HP 4stroke is now my Auxilliary engines back up because of this niggle