2 Stroke Powerband

Joined
Sep 19, 2014
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42
Location
Wisconsin
#1
So I've got an SXR 800 with quite a few mods, I bought this ski already built and haven't done much to it myself. It's an arm stretcher for sure, but the throttle response isn't exactly.... predictable. It feels like a 2 stroke MX bike when it comes onto the pipe. The powerband is a light switch: on, or off. After riding this ski all season, I've adapted and learned the ski. Problem is, I ride with the girlfriend and some inexperienced guys. It scares the hell out of them, to the point where they're hogging my superjet all weekend.

Is there any way to smooth out the power delivery? The powerband hits hard around 1/4 throttle and I'll be going full speed at 3/4 throttle. 3/4 to full throttle makes no difference - but that's a different issue altogether. Just wondering if there's anything I can do to either use the full throttle range, or stretch out that initial kick?

Ski details:
03 SXR 800
Porting by Z-force racing
Mild cut head
Factory B pipe
Vforce3 reeds
Carbs bored to true 40mm
Not sure on prop pitch

SXR.jpg
 
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Yami-Rider

TigerCraft FV-PRO
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#2
I'm no kawa expert, but it's probably something to do with the bored carbs and port timing. Running your b-pipe wetter will gain more bottom end if it's running on the dry side now.
 
Joined
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Houston
#3
Also what do the plugs look like, are the carbs tuned correctly? The impeller pitch will make a difference on low end torque and top speed, have you GPSed it to compare to a stock ski?

I had a big bore, ported SXR and the powerband was buttery and beefy through the low mid, although it retained the stock breadbox.
 

jeremy chambon

Need more power
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rockford MI
#4
Also what do the plugs look like, are the carbs tuned correctly? The impeller pitch will make a difference on low end torque and top speed, have you GPSed it to compare to a stock ski?

I had a big bore, ported SXR and the powerband was buttery and beefy through the low mid, although it retained the stock breadbox.
How would the pitch not effect this?
 
Joined
Sep 19, 2014
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Location
Wisconsin
#5
I'm no kawa expert, but it's probably something to do with the bored carbs and port timing.
This was one of my theories as well.

Also what do the plugs look like, are the carbs tuned correctly? The impeller pitch will make a difference on low end torque and top speed, have you GPSed it to compare to a stock ski?
Plugs looked normal, and I didn't mess with the carbs at all. I know my way around a single carb, but this is my first dual carb ski. I haven't messed with them, because this engine builder is well known and tuned it himself.

The weather is getting cold up here in Wisconsin so I just winterized it and put it away in storage last week. I was just seeing if you guys had any initial thoughts, to give me a starting point next spring. I may end up calling the builder and asking if he remembers the ski, and has any suggestions. It was built a couple years ago.
 
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Joined
Nov 13, 2006
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318
#6
dual carbs adjust just like singles,only synchronizing is an extra step.
known issue with the wet pipe you have.
try opening the water screws a bit more and see if it helps.
water injection will help out also.
talk to zforce about the port job.why recut the head? port timing etc...
your bored carbs and reeds have little to do with this.
a steeper prop will help tame the power band but you need to check max rpm's as well as speed before you start changing stuff.
 
Joined
Aug 2, 2011
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Location
Lake Havasu City AZ
#12
the cheapest thing you can do without putting a lot of effort and thought into it is try a pump nozzle from a 750sx. they have a larger exit diameter. the power will come on sooner and run out sooner.

Im not a fan of putting a bunch of water in the headpipe, makes the engine really flat. id run the headpipe as dry as possible to make the most power possible, then set up pump to give you the power delivery you're looking for.
 
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Joined
Sep 19, 2014
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Location
Wisconsin
#15
You got a ski that one of the best SXR Tuners out there!!!!!!!!!!!!! Talk to Tim before you make changes. Tell him what you want done. He is a great guy.
This was the response I was hoping for. I was just looking for possible solutions with this thread, but wouldn’t be willing to drastically change the work of someone who knows 100x more than I do. I’m the first to admit, I’m no tuning expert
 
Joined
Jun 17, 2018
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Here
#16
Is that like all squares are rectangles, but not all rectangles are squares?

impellers (sans radial flow types) are propellers....but not all propellers are impellers. o_O:p
They are used for propulsion, yes. Sheesh, you really are an engineer, eh? Props push, impellers create suction. It's not that hard. We really gonna do this?
 
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#18
They are used for propulsion, yes. Sheesh, you really are an engineer, eh? Props push, impellers create suction. It's not that hard. We really gonna do this?
So according to you, there is no area of low pressure directly in front of an airplane propeller?

Ya know, i reply to your posts in good fun, but you sure do like to argue semantics for someone with so much real world experience. But what do i know, im just an engineer...
 
Joined
Jul 29, 2011
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#19
So according to you, there is no area of low pressure directly in front of an airplane propeller?

Ya know, i reply to your posts in good fun, but you sure do like to argue semantics for someone with so much real world experience. But what do i know, im just an engineer...
Aren't you supposed to be driving a train right now?
 
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