rpm loss

[noahron]

I have a 1999 35 hp Johnson 3 cyl.
every once in a while I loose rpm it will drop to 3000 rpm and stay that way for a while, some times it run fine for days! than bang loss of rmp again.
I changed plug,fuel filter, even the power pack! no difference.
Doe's anybody have any ideas it has spark on all cyl.
it idels fine and will troll all day but no top end sometimes,
thanks
Noahron

[boats.net]

Check to see if loosing fire on a cylinder with a timming light, check for fuel restrictions.