Great rpms but diesnt plane

[Scooter1824]

Have a 1973 Volvo penta outdrive with a 302 mercruiser gets up to 4200 rpm's but will not plane. Any ideas ?

 

[saf]

Did you confirm the tachometer readings?

 

[Scott Danforth]

First, welcome aboard.

next, would need background on the frankensteined motor and drive.

would need to know what this frankensteined driveline is installed in? is it a 17' runabout or a 30 foot pocket cruiser

has the motor been serviced?
is the compression up around 140psi in all cylinders?
do you have the right prop for the setup?
has the prop hub spun?

 

[gm280]

Yes I was thinking a possible spun prop hub just from the comment...