1990 Yamaha 90

[Trevrich855]

Battling a issue with my 1990 Yamaha 90 2 stroke. The boat will get on plane, very sluggish. Once on plane it’s not hitting full power and I feel a thump of extra power every now and then. CDI box is good, coil packs are good, spark plugs are new, reeds are good,carbs cleaned, fuel pump brand new, fuel lines good, 120 on all 3 cylinders. I also hear a ticking/knocking noise, doesn’t get louder the high rpm’s turn its just there. Any pointers on what to try?

[Jason2tpa]

I’m assuming that prior to this issue there were no other issues….motor running at peak performance? Fuel, spark, compression….the 3 major outboard systems to troubleshoot. Sounds like you’ve got spark and compression which narrows things down…Though the tick/knock noise you described doesn’t sound like a fuel related issue. Can you pinpoint its location?

[ausnoelm]

Check spark on all cylinders.

[robert graham]

Clean plugs, run motor hard, shut motor down quickly during poor running….then pull plugs to inspect for which plug/ cylinder is missing…..sounds for sure that motor is running on 2 cylinders for some reason….are you sure carbs are really clean?