07 90hp two stroke low rpm's?

[pbois]

So I purchased a 07 yamaha 90hp two stroke used with 230hrs in 20" shaft to install on a 16.5 wahoo. The engine came out of Florida and is in excellent shape. After install we took the boat out and could only get it to 4500 rpm's after trimming. The boat moves fast enough but should be pushing 5500 rpm max. I completely drained the entire fuel tank which appeard clean. I also replaced all the fuel lines back to the tank to make sure I had no fuel problems on start up. The engine has a stiletto ss prop 13.5x17pitch that came with the engine. I was wondering if I shuld bring the pitch down to a 15? Funny thing is the last motor on the boat was a 75 merc and that had a 13x19pitch that screamed. Anybody have any thoughts?

[99yam40]

hard to say what boat this motor and prop came off of
Could it be a stolen one or do you know if it came off of a boat similar to yours

[TownsendsFJR1300]

If you go to this web site, it should get you in the ball park with your boat/motor combo;

Outboard Performance, Performance Bulletins | Yamaha Outboards

[99yam40]

Sorry about that I was just reading about some stolen motors
but you never know

[pbois]

the closet yamaha bulletin shows a 13.25X16 using the same engine

[TownsendsFJR1300]

A slightly smaller and higher revving prop.

If you have a prop shop nearby, you may want to bring your info/data there and get their opinion. You likely need to replace the prop anyway...

I'm sure they can give a good idea how much RPMs change with a different pitch/ diameter, etc...

I did that (^^^) when I changed a very incorrect aluminum prop to SS.

[Pbailey15]

Can't remember the prop, But I had that setup in 1988. 16' Yahoo Dual Console. 2 stroke Yamaha. 5600 RPM as I recall. Maxed out at 60 mph with one person and minimal gear.

[pbois]

***, pbaily. this boat w 3 people went about 30mph, i gotta try a diff prop

[pbois]

I want to thank everyone for their input. I replaced the prop with a 13.75X15 aluminum and the boat did 36mph at 5500 rpm w 2 people on board. Good enough for me, thanks

[TownsendsFJR1300]

Tks for the update, boat safe!