20 cc with F150 what prop are you using

[Jonhybrid]

I Recently purchased an 88 20 cc with a F150 Yamaha. The tach on it was off. I just install a garmin and installed the nmea 2000 cable to the motor and found out at WOT I'm only running at 4900 rpm. Cruise at 4000-4100 at 28-30 mph. The current prop is a 13 3/4 x 19P. I'd like to know what prop people are running to help me dial it in. The motor is at the right height in the water. Any info would help.