8 hp johnson WOT slow?

Any ideas on a 1991 8hp johnson---runs smooth at idle--only does 8 mph on a 12 light alum boat....doesn't seem to rev to its highest rpm.
Remer and Sherry Collins, August 2011


done
Check the pitch of the prop, this is like gearing, if to steep you will not reach max revs, if to shallow will over rev.

pedrodeltorre, October 2011