35 Merc A couple of Qs

[sogafishin]

I have a 1986 Merc 35 that purrs like a kitten.Hardly any hrs gor a great deal on it too but anyway when I push the controls all the way down wide open it actually looses RPMs.Almost like the butterfly in the carb is going too far.I can back of a little and it will push my 15ft Fisher Marine aluminum boat 27mph.I jumps out of the hole like a bandit.Is the timing going to far advance or is it a carb/linkage problem?Does 27mph sound like it is getting maximum RPMs?I have a 15 pitch Husler prop