I have a ?99 Yamaha F100 that I am recently having a problem with. The motor has unknown total hours, and has provided me approximately 1300 hours of fairly trouble-free service over the last 5 years
Last trip out, as I was heading in across the bay I bumped it up from cruise up to 5000 RPM. After about 30 seconds or so, the engine suddenly bogged way down. I immediately backed off throttle and took it out of gear. No alarms, so I shut it down for a minute. Checked for obstructions to water intake, etc. and saw nothing. Started the motor back up and it is running rough with a loud knock that gets louder and faster with increased throttle. Power was lacking ? it would run at maybe 50% power with intermittent spots of hesitation on acceleration. Limped in and put her on the trailer. Checked the dipstick and noticed a very slight amount of water/oil slurry on the upper shaft of the dipstick. None seen down on top of the main body of oil.
Once at home, after sitting for a day I checked the dipstick again and noticed some fine dark particulate (felt smooth between fingers) in the oil on the dipstick (possible comtamination from the cylinder, I assume?) The oil was clean and fairly new prior to this trip.
Difficult for me to tell the source of the knock since the metal conducts the sound so well. Could be from top end (valve?) or bottom (connecting rod?)
Checked the compression on warm engine with throttle open.
Cylinder #1 : 145psi
#2: 120psi
#3: 150psi
#4: 150psi
I know #2 is a little low, but it is within the 75% rule, so it seems to me that the head gasket is likely not the culprit.
What do you guys think?
Last trip out, as I was heading in across the bay I bumped it up from cruise up to 5000 RPM. After about 30 seconds or so, the engine suddenly bogged way down. I immediately backed off throttle and took it out of gear. No alarms, so I shut it down for a minute. Checked for obstructions to water intake, etc. and saw nothing. Started the motor back up and it is running rough with a loud knock that gets louder and faster with increased throttle. Power was lacking ? it would run at maybe 50% power with intermittent spots of hesitation on acceleration. Limped in and put her on the trailer. Checked the dipstick and noticed a very slight amount of water/oil slurry on the upper shaft of the dipstick. None seen down on top of the main body of oil.
Once at home, after sitting for a day I checked the dipstick again and noticed some fine dark particulate (felt smooth between fingers) in the oil on the dipstick (possible comtamination from the cylinder, I assume?) The oil was clean and fairly new prior to this trip.
Difficult for me to tell the source of the knock since the metal conducts the sound so well. Could be from top end (valve?) or bottom (connecting rod?)
Checked the compression on warm engine with throttle open.
Cylinder #1 : 145psi
#2: 120psi
#3: 150psi
#4: 150psi
I know #2 is a little low, but it is within the 75% rule, so it seems to me that the head gasket is likely not the culprit.
What do you guys think?
