Is it possible to set your Rev-Limit too high?

[John_Ciocca]

1994 701 Superjet b-Pipe 170 psi.

Just installed an MSD and cranked the rev-limit to the max. On my Pro-Tec modified CDI I had the limit around 7500 and I had no bottom end issues.

With the higer rev limit the prop seems like it does not hook up as well when coming out of the water at low speed. High speed everything is fine.

Is it possible that spinning the prop at 9K at low end kills some bottom end hook up? Or is it my skat 9/17 standard just not good enough at 9K (low end)?

 

[robertg]

Did you change the cdi and impeller at the same time? I don't think your engine will rev to 9500 rpm without a rev limiter.

 

[John_Ciocca]

Did you change the cdi and impeller at the same time? I don't think your engine will rev to 9500 rpm without a rev limiter.

No you don't understand. I did not change my impeller. I changed my modified pro-tec cdi with an MSD CDI.

I had the pro-tec cdi set at approximately 7500 rpm or so. When the ski comes out of the water and revs to 7500 (with the pro-tec cdi) the skat 9/17 seems to have good low end grunt and hook up.

However, now that it revs to 9K rpm when it comes out of the water at low speed (like jumping wakes) the hook up and bite seem off.

I was just wondering if anybody else has experienced something like this and if my impeller is no longer a good match at the higher rev limit...or am I crazy?

JC

 

[robertg]

I don't think it has anything to do with the rev limiter. Just because your rev limiter is set to 9000 RPM, it doesn't mean your engine is going to rev that high.

When your rev limiter was set to 7500 RPM did you hear it hit the limiter? It kind of makes a noise like di di di di di... when the rev limit is reached.

 

[Waste Land]

Your ski isnt reaching that high of an RPM when just taking off. Prolly not even hitting it on WOT throttle runs in the water. I've had less mods, and more mods then you and and have only hit the limiter in the air when i was being careless.

 

[John_Ciocca]

Okay....you guys are correct. I am not hitting the limiter it does not go "da da da" when I leave the water.

It does rev higher than where I had my pro-tec set because with the pro-tec installed it did go "da da da" when I left the water.

So I guess with the prop I currently have (9/17 standard) it works well with the limit lower......but not as good with the limit higher....Hmmmm? (low end messing around leaving the water only..of course).

 

[Waste Land]

your rev limiter has nothing to do with your prop spin on take off....your not getting near it.

I think its all in your head...its been slipping all along and you just noticed when testing out new parts...it happens tot he best of us

 

[keefer]

Ditch the 9/17 and get a Scat Swirl or a Solas Concord. Turn that MSD back to about 3/4 of full turn and you should be fine.

 

[John_Ciocca]

Ditch the 9/17 and get a Scat Swirl or a Solas Concord. Turn that MSD back to about 3/4 of full turn and you should be fine.

A friend of mine is doing a 650 to 701 conversion right now and has a skat swirl cutback. He said I can try it so I will find out how it works this weedend.

I agree with you Keefer, 9K just seems too high for the way I ride. My engine seems like it screams when coming out of the water. It's probably me not being used to letting go of the throttle when unhooking the pump. I guess when you hear the "da da da da" it reminds you to let go. I will back it off.

JC

 

[kevbo]

You are correct about the pump having problems working at high rpm, all 144mm props will be boiling water at 9000rpm. Your Skat 9-17 is still a good prop but the new styles are better in this regard. Turning down the rev limiter will get you better low speed hook-up with any prop.

 

[Waste Land]

a 701 with a pipe and some compression is hitting 9k in the water at "low speeds"??????????

 

[kevbo]

His problem comes from dropping the pump in the water while its spinning 9000rpm. The pressure at the leading edge drops too low causing the water to boil. Slow down the prop and it primes faster, getting off the throttle works best.

 

[John_Ciocca]

His problem comes from dropping the pump in the water while its spinning 9000rpm. The pressure at the leading edge drops too low causing the water to boil. Slow down the prop and it primes faster, getting off the throttle works best.

Thanks guys....this is what I though but it always nice to hear it from someone else.

JC

 

[Waste Land]

prop seems like it does not hook up as well when coming out of the water at low speed. High speed everything is fine.

:slap:

Why would he be at 9000RPMs at low speed. If his prop is spinning at 9000rpms in air...he needs to be off the throttle anyway after leaving the water

 

[sflsurfrider]

i think if you learn to control your throttle, you can leave the limiter cranked clockwise.

rev limiters are gay. might as well install training wheels.

 

[Big Kahuna]

ok, here is my take on this, first, I doubt your hitting 9k RPM's but that is irrelevent. When you were running the protec CDI with the RPM's limited to 7.5k and your ski left the water and it hit the limiter, when the pump comes back in contact, the RPM's have been pulled down it is easier for the motor/pump to get going again, if the RPM's are much higher when the pump comse loose you get more of a braking effect when the pumps comes back in contact with the water, water does not compress, and at faster prop speeds it is trying to compress the water which it cannot do........ This is just what I have come up with over the years.... I have found it best that when your pump leaves the water, it is best to let off the throttle and come back on throttle as soon as your pumps makes contact. If you race this is something that you kinda learn to do without thinking about it, especially in the surf. It is all about throttle control