1997 Yamaha 30hp knocks in high speed idle

[mattanderson93]

I have a 1997 2-stroke Yamaha 30hp outboard with a ton of hours on it. I inherited this boat from a family member who did not take very good care of the motor. This summer when I went to fire it up, I noticed two major problems with it. The first problem was that when the engine is revved in neutral, there is a very loud knocking sound, almost like one of the pistons is hitting the cylinder wall or something. But when I put the engine in gear, no knocking sound. The second problem was that when put in gear, the engine ran at trolling speeds beautifully, but when given any more gas than that, it would stall out almost immediately. My very little experience with engines tells me that it could be anything from a spark plugs to a clogged carburetor or bad fuel lines. It has a brand new fuel filter in it, so I don't think that is the problem.

If anyone has any ideas on either of these problems, or could suggest a good place to start looking, I would really appreciate it.

 

[99yam40]

Re: 1997 Yamaha 30hp knocks in high speed idle

1st off do not rev motor in neutral, bad for motor.
Next test compression, spark, and timing
If all is well check fuel pump and lower unit.
Then pull and clean carbs and adjust as service manual call for after reinstalling them