prop trouble

[G3yamaha90]

Hey Guys, I have a 90 hp 2 stroke with a aluminum prop 13 1/4 x 17 which used to turn 5500 rpm and run great. The prop got bent so I bought a new one which is also aluminum and the same size, the only difference is the brand name. So I put the new prop on and ran the boat and now it is slow out of the hole and will only turn about 4800 rpm so lost some speed also. I am stumped ! Does anyone know what the difference could be ? Any help would be appreciated. Oh yeah the old prop had a letter Z at the end of the size stamped on the prop, the new one is a Solas and has The letters RB at the end of the size on it. Does this mean anything ?

 

[180shabah]

Re: prop trouble

Does anyone know what the difference could be ?

When you changed prop manufactures and designs, you need to start over on the pitch. You need to give more details on both the old and new prop. does the new prop have more blades and or a larger diameter?

 

[steelespike]

Re: prop trouble

I'm a little surprised a 700 rpm difference.It would be interesting to
see your max speed with the old one and that with the new one.
Speed in relation to rpm. You might try to find a description of the new prop.
See if its just generic or has some meaningful info.Sure seems like it is pretty agressive.

 

[G3yamaha90]

Re: prop trouble

I said it is the same diameter and pitch. They are both 3 blade props the new one is a Solas and I don't know what brand the old one is. The point is they are suppose to be the exact same prop , if they were different sizes I wouldn't be asking for help !

 

[G3yamaha90]

Re: prop trouble

Yeah the speedometer isn't working at the moment but it feels alot slower due to the loss of rpm's

 

[steelespike]

Re: prop trouble

I said it is the same diameter and pitch. They are both 3 blade props the new one is a Solas and I don't know what brand the old one is. The point is they are suppose to be the exact same prop , if they were different sizes I wouldn't be asking for help !

No need to be so testy. Many times a person refers a prop being the same size only refers to pitch. You did say same size Not same diameter and pitch. We are searching to help you.Is there any chance if you tipped the motor up you may have dislodged the throttle cable.Or perhaps you struck something hard enough to damage the throttle linkage.
Did you have the cover off perhaps dislodging a plug wire.
There is a throttle device that limits the throttle in neutral perhaps it has been damaged
or simply went out of adjustment.Was the old prop a little tired?Starting to show serious paint wear and or a few light dings?

 

[G3yamaha90]

Re: prop trouble

I guess it is possible that there is a different problem but I think the boat was still running fine the day the prop was damaged (log). I guess I should put the old one back on and run it to be sure. There was a vibration due to the bent up blade so I didn't want to run it alot and mess up something else !

 

[steelespike]

Re: prop trouble

bump^

 

[Silvertip]

Re: prop trouble

Just because the prop is the same diameter and pitch BUT from a different manufacturer does not mean it will perform the same. In some cases it is better and some cases it is worse. Why? It is called design! Props have many design characteristics besides diameter and pitch. Rake, blade shape, blade area, cupping, finish, are just a few. All of them can add to or detract from performance when compared to other "similar" props.

 

[wellsc1]

Re: prop trouble

I too have a Yammy 90 hp 2-stroke. I tried a going from the stock aluminum 13-1/4" x 17 pitch to a SS 13-1/4" x 17 pitch, but different manufacturer. That's where I starting my education about props from HWSII and others. My initial experiences were similar to yours.

If your AL prop is the stock Yamaha prop, it's semi-clever lobes. Going to a SS prop with full lobes with additioal rake and all does make a difference.

I returned the diff. manuf. SS prop, got a Yamaha SS semi-clever 13-1/4" x 17 pitch, but still had bad hole shot. What's when I talked to my motor mechanic and got the low speed jets cleaned. That made world of difference. Boat almost jumps out of the water and already has hit 39 mph at 5200 RPM.

Bottom line - start with Yamaha semi-clever prop and clean carbs. IMHO