Need a better prop?

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#1
I'm pretty sure I'm spinning my 9/15 prop in my 735cc freestyle port 701/ X2. FP exhaust. lighten flywheel MSD I installed a intake grate but I'm not feeling the ski hook water until it reaches some decent speed. Actually this ski is fast in the mid and top end but if a 9/15 was meant for low end I'm not feeling it. I think I have more motor than prop. What is another option?
 
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#3
but if a 9/15 was meant for low end I'm not feeling it.
I think what you want is an impeller that accelerates better?

There are 2 different ways to describe acceleration on a watercraft.
An impeller can accelerate from idle to ~7000 rpm quickly, or the
watercraft can accelerate faster in feet/sec.

An old Solas with 12 degree leading edge may accelerate faster in ft/sec
than an old Skat Trak with an 8 or 9 degree leading edge. This is just a simple
example, there are many other details that contribute to impeller design.

The most important detail is: Does your impeller allow the engine to make
peak horsepower. If the impeller allows the engine to make peak HP
plus a few hundred rpm, there isn't much room for impeller changes.
(Unless you want to accelerate through the rpm range faster).

Increases in over-rev (past peak hp) will give you opportunities to possibly
increase ft/sec, or mph. Each requires more HP, or some extra power that
allows you to tinker with your impeller. But make sure the changes allow
the engine to still make peak HP.


Bill M.
 
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#4
I used my Yamaha spec book for measuring clearance when I installed the prop, I don’t remember but it was well within yamaha specs. My understanding of the low pitch on the 9/15 was it allowed engine to rev quicker. That might work on a lower hp engine. When I slide a turn for example I’m nearly stopped in water, to gain movement again I find the engine revs 1/2-3/4 throttle with no hook up. I have nearly the same motor in my B1 with a 10/16. There is no stalling on the B1 like my X2.
 

SXIPro

JM781 Big Bore
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#5
I had a 9/15 in my ported 735, BPipe, ADA Head, lightened flywheel, MSD...yadda yadda yadda and it had instant hook up on the bottom end. It just leaped out of the water.

SJ though, not X2. When I stepped up to a 781BB I plopped in a 10/16 based on the recommendation of the engine builder.
 
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#6
Dave from Impros recommendation on the 9/15 but that was on a stock 701 with X2 pipe. I’m on flat water so every small detail shows up. ie: tuning an engine on flat water vs rough water. I’m tempted to put the open grate back in. The scoop only helps in choppy water at speed anyway. Does anyone still offer the poor mans mag conversion for the 140 pump. I see Raddudes carry the spacer plate.
 
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#7
I think what you want is an impeller that accelerates better?
YES FT/sec. I don't need to reach 7,000 rpm plus and go no where. Prop degrees are tricky yes but if they can be described like a boat prop then yes i need a arm jerking ski boat style prop which have taller pitch but top speed is sacrificed.
 
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#10
The stock X2 hull is not the greatest.

YES FT/sec. I don't need to reach 7,000 rpm plus and go no where.
In order to have a reliable engine, you need to match the exhaust port duration
with the pipes tuned length. On many engines the peak HP is located at 6500
to 7100rpm. When your pump limits peak rpm to less than peak hp rpm, the
engines reliability can suffer.

yes i need a arm jerking ski boat style prop which have taller pitch but top speed is sacrificed.
The easiest way to get "Arm Jerking Power" is with good carburation.


Bill M.
 
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#11
People can run the 9/15 on 650s. I think you need to pitch up. When I had an X2, Dave recommended me a 10/16 when I swapped to a 750 (jet pro pipe, mild compression). The impeller did great all around on it. I later built a ported 800 with blackjack carbs, +6 timing plate, 180 comp. It still pulled well but ran out up top. I feel like if he recommended me a 10/16 on basically a stock 750 with a pipe, that you would need at least this on your yamaha set up.
 
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#12
I’m fully aware of two stroke rpm hp correlation. I run snowmobiles and can tell you the correct weights, spring and altitude all must match rpm range for maximum torque. I’m describing an engine that has been professionally ported using a Superjet expansion chamber. Etc etc.. The characteristics of this acts like I’m spinning the prop with no forward movement coming off a hard slide turn stalling the ski in water and attempt to gain quick forward movement again. Mid and top end acceleration is awesome. Perhaps my jetting is a bit rich. New motor, 152.5 m 120 p 28 psi pop. I don’t feel that this engine needs fine tuned to gain every ounce of performance as much as a major change in prop. I’ll go back and make tweets to carb and water screws first but very tempted to opt for a different pitch. I not saying this prop is no good but maybe not matched for this engine. I’ve read more than a few guys reported over on PWC site state the same thing, a 9/15 just spun the motor. Appreciate any input I can get.
 

SpaceCowboy

breaking something
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#13
If the motor is accelerating fast through the rpms you’re spinning the prop. You can play with jetting but you won’t get more traction that way. 10-17 or 11-18. Also how set back is your impeller to the vanes of the stator?
 
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#14
Set back I can’t say. It’s a 9/15 hooker big hub. No changes made to pump stator or impeller. Straight of the shelf impeller. I know nothing about pitch angles. But if a Hooker 9/15 was meant for low end and Hooker 11/17 for top. I’m confused. I’m very pleased with my Jetmaniac freestyle port mod pipe B1 with a 10/16.
 
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#15
The characteristics of this acts like I’m spinning the prop with no forward movement coming off a hard slide
turn stalling the ski in water and attempt to gain quick forward movement again.
Before this post, I was under the impression that your problem occurred in
a straight line.

Now it sounds like your issue is X2 hull related (unless your impeller's leading
edge is dinged up a little).

It has been too long since I used to ride X2's, but the X2 rider I tune for uses a
Jet Dynamics grate (not an old one). Ask someone else about their experience
with that grate, and if it will help your problem.

X2 Handling is his department.

Bill M.

Ask about tubbies too.
 
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#16
On a separate post X2 Intake grate I asked and got a reply to use RCJS Tri Scoop. It works good on choppy water for sure. Describing this lazy low acceleration with words is a bit tricky. I mentioned the slide turn because at no other time is the ski in contact with water at such a low stall speed and at its worst position to pull in water. If I attempt to set up for wake jumping the ski doesn't have the same hard pull as my B1. If i'm on flat water and try to accelerate quickly I don't notice the arm pulling until I'm up to speed say 20-25 mph then hang on its all top end. I have an aluminum exit nozzle that i've bored out to 83mm and get rid of the plastic stock one. I will try that this weekend.
 
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#18
IF is the question, it’s a lot less money to try carb, pipe tuning and nozzle choice than impeller change. IF it does get worse then my original suspecien is correct but what pitch is the next question. Dave at Impros is gone. I called but if a pitch change is needed I didn’t get a confident answer to exactly what pitch I need. The trouble with the X2, few play around with them in this way. Waaay more pony than what that ski was ever designed for.
 

SpaceCowboy

breaking something
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#19
You have a 140 pump vs a 144 and a 9/15 hooker is what you’d run in a Yamaha 144. I’d bet my money you don’t have enough prop. Go ahead and fiddle with the rest of the stuff. You should be able to feel pump vs engine tuning. Put a spacer between the impeller and pump. See if that nets you anything.
 
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#20
Interesting I’ve never understood set back if that’s what your describing. How thick of washer do recommend trying? To be clear your stating a larger gap between exit side of the impeller and pump fins?
 
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