2003 150 hp ox66

[Jeffhale]

Hello everyone
I just purchased a 2004 Godfrey Santana 2500dc pontoon it 26.5ft long and it has. A 2003 vx150tlrb ox66 outboard wide open throttle is 2800 rpm 20 mph
It had a stainless 15" diameter with a 17 pitch prop In neutral it will rev up to 4900 rpm so I assumed wrong prop. So I purchased a 15" diameter 13pitch prop I got 3200rpm and 23mph new to boating. Need help any ideas. Thanks

[scofflaw]

Should we assume the PO had nothing to say about this ?
How clean is the bottom of the boat and running gear ?

[Jeffhale]

The tunes are not terrible but could use a cleaning but shouldn't the motor still come up to 5,000 rpm regardless of speed thanks

[99yam40]

running a motor in neutral is never good on it, some motors will try to protect against running high RPMs in neutral.
I have no idea is yours will do that or not.

start with basics, compression , spark, and timing.
fuel pressures is another thing to test.

best would be to find a shop with the proper test wheel for that motor to see if it can spin that up to proper RPM sitting in a tank.
that will tell you quickly if the motor has a problem .
If it does not then start looking for a rigging or prop problem

look for a rig like yours here and see what prop they used and the RPM and speeds
Outboard Performance, Performance Bulletins | Yamaha Outboards

[BQUICK]

I bought a 1988 200 cheap once that had a Yamaha replacement powerhead in it. It would barely plane a 245 Slickcraft even with a lower pitch K spline prop from a 115 that had a M spline put in it.
I get it home and see throttle is barely going to 2/3 throttle. Turns out when the new powerhead was put on they put the oil pump link from the carb on the wrong side of the oil supply hose causing it to hang up. Flipped it to other side and it got full throttle.