First and foremost, 75hp is enough to push that boat a lot faster than
8mph. You should be able to ski behind it. Beyond that, any number of
things could be the problem. For one, are you sure you remember 2500
rpm instead of 4500-5500 maybe? At 2500, it shouldn't sound like full
throttle. You didn't run over a plastic bag, or snag a crab trap, or
forget to haul your anchor, or have a bilge full of water do you? Or
you could have spun your prop hub, meaning the hub has broken loose
and no matter how fast your engine turns, the hub slips inside the
prop and the prop won't spin very fast.
Anyhow, those are a few possibilities. I'm sure other folk here will
add more.
Rick

On Sun, 18 May 08, "Jim Swope jr" wrote:
I just bought a 1971 Glastron V-170 Crestflite and it came with a 1983 75
horse Evinrude. The markings on the prop say 13-1/4X17.
The engine seems to be running fine at high and low rpm's.I cant hear any
missing. It cruises nicely at low rpm's but when I give it full throttle It
sounds like it is at full
throttle, im getting about 2500 rpms if I remember right. Also with the
cover off and manually holding the throttle at full bore I can only get
about
eight miles an hour out of it according to my hand held gps. At any rate it
goes pretty slow and Im not sure why. Is this engine too small for this
boat.
The recomendation for this boats says not to use any bigger than 125 horse
so Im thinking 75 should be sufficient.I've tried adjusting the plane in all
different positions but dosnt seem to matter much
and get no noticable increase in speed. Any suggestions would be happily
appreceiated.


Thanks.... Jim