Mine is a 4 stroke 9.8 and also has a little hesitation when I open it up, especially if I do it gradually. My gut feeling is the carb and the high speed jet. Perhaps a bit of water or crud. I often have to drain the fuel filter about every two or three weeks because of water. My gas tank has a replacement cap without the gauge and a rubber cover to further protect it from rain. Perhaps this is anal or excessive, but it seems to help and rowing a RIB isn't one of life's great pleasures. At the end of the season I drain the carb and soak it with WD40, again it seems to help.