Excessive rpm w/stock prop

[MossBoss95]

I have a 1995 basstracker v17 and a 40hpmerc oil inj. I have owned this boat for 10 years and the prop is original.

I have recomended rps at 5500 and the tac is reading 6000 @ wot.

I was wondering what people are using for props on their 40's and if a larger prop is ok to recuce the rpm's. This is not a fast boat but I usually get 28-30mph gps.

Any opinnions or thoughts would be great.

Thanks,

Mossboss

[marine_man]

Yes.. you'll need a larger pitch prop... what size are you currently running?

You'll loose some holeshot with the larger prop, but it should still be more than sufficient, and you'll actually pick up a little speed by going to a larger prop. I'd guess you'll have to increase your pitch by 4", but that's somewhat dependent on what you currently have.

marine_man

[MNice]

If you're happy with the performance, why not back off the throttle a bit?

[LocalGuide]

Quote:

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If you're happy with the performance, why not back off the throttle a bit?

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Haha, Thats easier said than done!

I do the same on our motor, It runs about 2,000 RPM over the recommened RPM. I do back off the throttle a bit when running the motor for a long time (10+ minutes) otherwise I shove it to the floor.

Its probably not a good thing that it runs that high, but when skiing/tubing its nice to have. Since our boat motor is at the minimun hp (140hp) its so much easier to get a person up for tubing and skiing with that pitch insead of an increased pitch on the prop.

And like the quote says, try and back off the throttle just a bit (sometimes!)

[marine_man]

So... where does this 2,000 RPM over the limit put you? I'm pretty sure the johnson 140's (judging by your avatar picture) hits the rev limiter at 6200 RPM... and the normal operating range on this motor is between 5500 and 6000... There's no way you're going past the rev limiter, unless you've removed it, which would void your warranty...

marine_man

[Hookmaster]

I'd suggest you take it to a shop and have your tach checked to make sure it is accurate before you start trying different props.

[Valv]

If tach is at ) it cannot be "slightly" off. They are correct or way off or no work at all.

[LocalGuide]

I think range is between 5700 - 6200RPM but it could be what you stated. I didnt change anything, I can get it upto 6400 when trimmed up to the max. The motor is 140 Johnson 4-stroke. When trimmed down just a bit its RPM is at 6150. So Im not to worried, just the times when I like WOT!

But a stainless steel prop does really help performance too!

[MossBoss95]

Thanks for the replys, I will look into the tac. I also think the prop might be too small after filing the edges removing nicks.

Thanks

[Doonbuggy]

MossBoss - I'm looking at the same thing as you. If you do a web search on finding the right propeller you will find some great info. I was quickly educated.

The general rule of thumb is that for every inch you add to your pitch, the rpms will go down about 200.

So if you go from, for example, a 17 to a 19 your rpms should drop about 400. That still might leave you a bit higher than you want so you might have to go one more step up.

And yes, you should see a little more top speed without losing any or much on your hole shot.

DB