Help with RPM

[kb3gup]

Hello I have a 1992 Johnson 60 hp (VJ60TLENE) with a 13-1/4 X 17 prop. I recently replaced it with the same model/brand prop, but I'm not getting the same performance out of it (around 4900 RMP WOT). It looks a little different then the old one (the blades are fatter but not as long.) My friend told me just to trim it up a little at WOT but I'm a little nervous because I don't want to over rev it. Does anyone else suggest this? I have been running it level, but not knowing if my engine has a rev limiter or beeper I've been hesitant to try. Thanks.

 

[Irv964]

Re: Help with RPM

Hello I have a 1992 Johnson 60 hp (VJ60TLENE) with a 13-1/4 X 17 prop. I recently replaced it with the same model/brand prop, but I'm not getting the same performance out of it (around 4900 RMP WOT). It looks a little different then the old one (the blades are fatter but not as long.) My friend told me just to trim it up a little at WOT but I'm a little nervous because I don't want to over rev it. Does anyone else suggest this? I have been running it level, but not knowing if my engine has a rev limiter or beeper I've been hesitant to try. Thanks.

What max rpm is your motor rated for? I assume you have a tach? If your not reaching your max rpm that the motor is rated for with this current prop then by all means trim up and keep an eye on your tach to verify your not exceeding it. Most outboards run the most efficient at or close to the max rpm the motor is rated for, if your under the max by quite a bit then your motor is lugging and it is just as hard on it as overrevving. ...Irv964

 

[kb3gup]

Re: Help with RPM

The book says it should run between 5000 and 6000 RPM. I figure 4900 isn't bad but I'm just trying to get that little extra push out of it.

 

[steelespike]

Re: Help with RPM

Your motor will be much happier closer to that 6,000 rpm.You should trim out for the max rpm and speed.Once you have that let us know the figures.
We can figure if a prop change is necessary.Do you have power trim?

 

[Randybeall]

Re: Help with RPM

You have discovered the differences in prop design. Your orignal prop may have been to a prop repair shop that fine tuned it and got the better performance. By all means experiment with trim up. Your engine should be above 5500 rpm at least with light load at WOT. You may have to go as far as raising the engine, but that would seem unlikely. New prop, new headache. Maybe when you get everything adjusted right you will have better performance than orignally.