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I have a '97 90 HP Yamaha on a 17' bass boat. Yesterday while running at top speed, trimmed up on plane, I wanted to make a turn in the boat lane so I trimmed down and the motor made a small erratic knocking noise that sounded as though it was coming from the lower unit. I could feel it in the throttle handle but didn't notice any change on the tach. I stopped, brought the boat back on plane to full throttle, trimmed up and then again trimmed down as if to make a turn and again it made the knocking noise maybe a little louder and the motor felt like it hesitated but I still didn't notice an RPM change. I had someone by the motor and he said it definitely sounded like coming from the lower unit. Motor runs perfect at idle, low speeds, and wide open until trimming down. Any suggestions? I pulled the plugs and they all look good and the top of pistons look OK. Thanks for any help!
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Bill,
Could be the hydraulic rams - put a thin coat of water resistant grease (I use Mobil 1 synthetic) on the sides and also on the ends. Do this, of course, when the rams are dry. Other than this, check the obvious like prop nut tightness, trim tab, and lower unit bolts.
Good luck,
Ken K.
Beaumont, TX -
the first guy is probably right. The roller balls in nthe rams get dry and pop when trimming. Also check where the steering tube is and be sure that is ok.Comment
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