Johnson 6HP Seahorse on a 12ft semi V-Hull - top speed question

[texas_salt]

Whats up guys.

I recently restored a 6R-69M

-new plugs
-new wires
-new points (timed properly)
-new condensors
-new thermostat
-new lower oil
-rebuilt carb
-impeller in good shape
-50:1 gas/oil

Its on a 12ft semi V-Hull.

I've taken her out twice and shes running beautiful and reliable. Good/Fair spark on both cylinders.

EXCEPT, at WOT i'm only getting about 6-7MPH according to the GPS.

From my youtube research, I see guys easily doing 12-15mph on the same old motor. Now, i'm a big guy. 290lbs. So thats an obvious factor. Its also on a semi v-hull which I have read can play a role. Finally, and possibly the real culprit? compression is 60-70 PSI on both cylinders. Which I hear isn't great, but, eh.

So, knowing the above, does 6-7MPH at WOT sound about right? I just want to be sure i've ruled out anything mechanical.

 

[F_R]

Compression is low, but tolerable if it starts and idles OK

Speed is normal if you don't have enough horsepower to plane the boat. With your weight and considering the boat, I suspect that is true (not enough hp).

 

[texas_salt]

Its funny that it moves just as quick whether its just me on the boat or me and the wife and kid.

A little more speed would be nice, but its hard to complain considering the motor is older than I am

 

[oldboat1]

might pick up an articulated tiller extension, and operate from the middle seat when out motoring alone.

 

[texas_salt]

might pick up an articulated tiller extension, and operate from the middle seat when out motoring alone.

Was looking at those last night. I will definitely get one.

 

[Vic.S]

The maximum speed of a non planing hull is determined by the waterline length. There is a formula for calculating it which is given in the link below to Wikipedia although hull type and shape are also major factors..
Your 6-7 mph sounds pretty good. To go faster you will have to get the boat planing. I dont know if yours is a hull that will plane.

https://en.wikipedia.org/wiki/Hull_speed