Yamaha 25 x 2 stroke 1999

[bayentnsca]

I have a 25 here that starts well and operates fine at fast idle to full throttle.
The problem is at low idle where she will seem to kick back through carb like spark is firing too soon?
Seems just to be on one cylinder?
Has me and ob shop shaking heads.
I had suspected air leak but can not find it.

Engine 2
Yamaha 80 x 4 stoke 1999
When it warms up to normal goes into overheat mode.

Engine 3
Yamaha 60 x 4 stroke 2015
Alarm sounds when shift select / throttle quadrant is placed in nutral.
No water in separator.
Water is a problem since methanol added to fuel.
Tried high test and more water in it than cheap fuel.
Going to install big filter but still have alarm issue to deal with.
I am 2.5 hrs drive from nearest Yamaha marine dealer.
Thanks for any help.

[boscoe99]

I can only address the 2015 F60. Disconnect the water in fuel sensor and see if the alarm stops when the motor is in neutral. The sensor switch may be failed closed.

[rodbolt17]

the 25, fix the fuel/carb system.
the f80,fix the cooling system.
the F60 do as boscoe says.
see how easy this is ? .