40hp yamaha enduro

[theviking]

have a 40 horse on the back of a 4.2m tinnie.
splutters/ misses a bit on full throttle.
when you back off a tad its fine.
has done it all its life (well, since I bought it 5yrs ago anyway).
no change after servicing etc....

Any idea's?

[boats.net]

Not familiar with Enduro models but if they have a rev limiter then may have too small a pitch prop on it.

[99yam40]

have a 40 horse on the back of a 4.2m tinnie.
splutters/ misses a bit on full throttle.
when you back off a tad its fine.
has done it all its life (well, since I bought it 5yrs ago anyway).
no change after servicing etc....

Any idea's?

Too lean or a too rich fuel /air mix can cause the cylinder not to fire properly. Also a weak spark can do it too.
You will have to start testing things to see what is going on.
My C40 had that problem and I found out someone had drilled out the main jets, so I replaced them. But not until I measured fuel pressure/vacuum, and all the ignition voltages like the manual says