Low RPM Yamaha 60hp 4 stroke

[InstTech]

I bought my first boat last week. 2012 G3 pontoon with 60hp 4 stroke EFI. The guy I bought it from put muffs on it and it started and ran fine. He showed me compression test paperwork and everything looked good. I take it to the lake and I can't get over 3200 RPM and max out at 8 mph. I've changed the prop, water separator filter, the small filter, checked for kinks in the fuel lines and cleaned all 4 injectors. Also it starts fine with the muffs on out of the water but under a load in the water I have to idle up to get it to start. Don't know if that's normal. Any information you guys can give would be greatly appreciated

 

[99yam40]

not taking a trial run on the water is not good,
did you ask what RPM and speed the boat runs at WOT
do you believe the previous owner about the compression?
I would check compression and do a leak down test to make sure cylinders a sealing properly
check spark plugs for signs on problems when you pull them.
check spark and timing, along with fuel pressures