Hello. I have a 2001 Yamaha F115 4Storke that ran rough and alarmed at 5500-6000 RPM. I changed the thermostat (no help) and then changed 2 bad spark plugs. Under a microscope, one had a hairline crack in the insulator, the other had irregularities in the electrode and you could see where it had arced. With new plugs the motor smoothed right out, runs like a top until you open it up to 6000 RPM. Then it still seems to be running smoothly but after 20 seconds or so the alarm sounds (Overtemp and Low Oil LEDs on dashboard DO NOT come on). Slowing to idle kills the alarm and then you can increase speed again, as long as you don't go above 5000 RPM. <br />Is there an overspeed alarm on this motor? Would a prop with greater pitch slow it down so I could never reach the overspeed range? Manual says that 6000 RPM is top of speed range. I have never gone above that according to Tach.<br />Oil is clean and fresh, right up to proper level; and cooling system appears to be operating correctly. Any other ideas?? Thanks, Al
