Need Help with prop selection

[redspot321]

Heres the deal. I bought a used boat that runs great, but I think I could get some more preformance out of it.....
2004 Key West 1720 90hp yamaha
Currently at Wide Open Throttle (WOT) Im running 4600rpm and 36 MPH. no gear!! Trimed out...
From what I understand I should be running 5500rpm and 40-43MPH

Current prop >>> 13 1/4 X 18 pitch.
Proposed prop >>>>13 1/4 X 13 pitch prop.

Is this too aggressive of a drop in pitch? Im using the 200 rpm per pitch rule here.
Also the boat runs GREAT!! Starts up with the click of the key and smooth as can be. What else could cause this issue?

Thanks

[Bay Catt]

Beings this is a used boat you might want to check the throttle control linkage to see if it slipped and needs adjusting before repropping. To see if this is the case you will need to run engine at wot then try to move the trottle arm on the carbs to open up move, thus increaseing rpms. If this can be done adjust the linkage for greater rpms. If there is dead travel on the remote control box the linkage can be adjusted in there. If not the linkage can be adjusted on the cable inside the motor cowl. Make sure after adjusting that the throttle returns to the correct idle rpms. Also check with Yamaha for correct prop pitch.

[Bay Catt]

Just check for correct prop pitch. The correct prop size is 13 1/4 X 13.

[redspot321]

Bay cat, Thanks. Where did you get that info form? I called yamaha and they said pitch is customer preference, thats why boats dont come with them...... I wonder why the prop would be 5 pitches off? Its a yamaha preformance ss prop..


Also, with the throtle control, after 75% in the forward position there is no increase in rpm from 70% to 100%. Does this sound like it could be my issue?

Thanks again, I just ordered the new prop.

[Bay Catt]

Parts info can be found from the home page of Boats.net, Click on OEM Yamaha parts then you will be directed to enter engine info all you will get all the parts,(including the prop), in an illustrated form. Prop pitch is a preferance however there is a pitch range you should stay within. Over or under propping you engine will either put to much of a load on it or allow the engine to over rev. After you install the new prop try it out and if you still can not get 5500 rpm then check the throttle linkage adjuster inside the motor cowl.

[redspot321]

Anyone else want to chime in?

[cyrillefrenchy]

hello
i owne a 17 cobia center console bay with a 85 yamaha, about the same kind of boat and engine,the best prop for me is a ss 13x19 and she goes 41 gps at 5200 rpm full gas tank and only the driver.
also a 13.25x17 aluminium vortex goes the same speed at 5500 5600 rpm and better holeshot if passengers.
frenchy

[T-Bone]

Ken regularly referred people to Marcus Clements, who works for PowerTech propellers in Louisiana. I took his advice and have since purchased two propellers from them for completely different boats and applications. In both cases, Marcus "nailed" what we were looking for.

Start with their form on www.ptprop.com and forward your information to marcus@ptprop.com and see what he says.

[Funky Monkey]

Thank you ever so much, T-Bone!!! I couldn't ask for a nicer recommendation, my friend. Your support and Ken's are GREATLY appreciated!!

Redspot, something's definitely amiss, as your 90 reeeeeally needs to be turning more rpm. If you'd like, please, feel free to drop me a line any ol' time. I'd be deeeelighted to help you find the key to Key West happiness. Cheesy. Yeah, I know. hehehe

I think I still even have Key West's OH-fish-ul prop chart from 2005 runnin' around here somewhere, thanks to good ol' Wilson Scarborough at KW.

Thanks, again, T.

Marcus
One Half of the Hydrodynamic Duo
marcus@ptprop.com