Low RPM Performance?

[sloguy]

I have recently purchased a small (12') pontoon boat with a new 25 HP Johnson motor. After 8 hours of run-in I can only reach 4200 rpm at full throttle. I've checked that the carb is wide open at the full throttle setting. The Johnson handbook says this engine should attain its 25 HP at between 4500 and 5000 rpm. I'd suppose that the supplied prop (10 x 13) is not correct for this application but I can find no smaller pitched prop (say, a 10 x 10).<br /><br />Any advice? I'd like to have a bit more speed but am not sure if another prop would help. Also, I'm not sure if running the engine "loaded" in this way is detrimental.<br /><br />Thanks for any help.

 

[Solittle]

Re: Low RPM Performance?

First a welcome to you sir!!!<br /><br />You do need to get the rpms up as it is not good for the longevity of the motor to run with a max WOT less than recommended. If you can't find another prop take the one you have to a prop shop & describe your situation. They can repitch what you have.

 

[rickdb1boat]

Re: Low RPM Performance?

Personally,I would take it back to where you bought it and have them rectify the problem, whether it be the prop or a problem with the motor..<br /><br />BTW: There is an 11 X 9" prop available for your motor. Should do the trick..<br /><br />Michigan Prop # 011033 would be a good choice, as it has extra cupping for your toon motor..