Capri 1950 Prop size

[abbersfamily]

I have a 1999 Capri 1959 with a 135 hp engine. I currently use a 15-17 prop. I can go 20-22 mph at 3800 rpm +/-. Is it possible to use a larger prop, say a 15-19 or 15-21, to increase speed?

 

[Bondo]

Ayuh,..... Welcome Aboard,..... At 3800 rpms, it's already over-propped,....
Or the motor is severely under preforming,....
Wot rpms should be 4600/ 4800 rpms,....

Probably oughta start with a compression test on the motor,....