Went out fishing last Saturday for the first time since March. I know, that 's bad! Anyway, while running around through out the day I noticed my big motor was "pulsing" in terms of power as I was going from spot to spot. By pulsing, I mean you could feel the boat speed up then slow down slighty. RPM's stayed the same. Have never noticed this before. Nothing real dramatic but I noticed it. Was using a fresh tank of gas. It's a 1993 Yamaha 150. Any thoughts on what it could be? Motor started and seemed to be running fine other wise.