1995 Johnson 60 HP loses power above 3/4 throttle

[pontooner]

I have a 1995 Johnson 60 HP model J60TLEOC that runs fine up to about 3/4 throttle @ 4800 RPM - it will run all day at that throttle position. As soon as I push past that throttle position towards full throttle - it loses power ans drops down to 4000 rpm at full throttle. If I pull back to 3/4 throttle again, it jumps back up to 4800 RPM and runs fine.

[boats.net]

Check timing and linkages, be sure the timing advance is working through its full range. If all is good, remove and clean carburetors, be sure to properly link, sync and adjust them when reinstalling.