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1996xp performance mods- educate me

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CantSWIMbutSEAdoo

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Hello guys. Dunno why I waited this long to get on the forum because I’ve been riding the same 1996 xp for years. Love it btw but......

I’d like to get some more power out of it. I’m well versed on building power in Oldschool muscle cars but not anything that floats. I was thinking of spending ballpark 500$
My drawing board looks like this and If you’ve done any of these mods give me some feedback if you don’t mind

1. Mill the head (raise compression)
2.Possibly run E85 as an alternative to high octane gas. I know boaters hate ethanol but I don’t know why.
3. Waterpipe
4. Intake grate- Is there a balanced style? If it improves top speed and acceleration I’m cool with it.
5. ??????? What else can I do That’s effective?


Me n the boys are goin out to st Clair for a day when it gets warm so I’ve got at least till May before I’ll be riding the ol ski. That means there’s time for some mods
 
1. You are better off with an aftermarket head to raise compression.
2. No E85 and it will not do anything for performance but will be very hard on your fuel system.
3. A pipe is the best way to add performance.
4. Intake grate will not make your ski faster and can actually make it slower on smooth water. On rough water it will help keep the pump hooked up but it does not actually "make it faster".

Your two best and first mods should be a pipe with rejetted carbs and extended trim tabs.

Contact @Matt Braley here as he has all the parts and info if you want to buy good go fast parts.
 
Thanks for the write up I’ll be sure to stay away from E85. I’ll start looking at pipes, are pipes for skis like impellers? You get either top speed or acceleration but can’t really get both?
I’m a balanced style I’d rather see gains in both speed and acceleration over having the fastest mph ski on the lake or quickest takeoff

Been looking at impellers too. This ski could use one.
 
I agree that a good aftermarket pipe setup correctly is best way to make power. Factory Pipe and Rossier are the favorites of most. The carbs will have to be rejetted. You will want to run premium fuel especially with a head that has higher compression. You also want to start with a fresh/strong engine.

Without a pipe there are still things that you can do. An aftermarket head with free flowing flame arrestors and rejetted carbs will give you a difference that you can feel especially if you reduce the mass like a lightweight pto and/or lightened flywheel. You can send your grey box to me for $50(20 of it is priority shipping back to you) and I raise the rev limit, put the #5 timing curve in it and advance the timing.

First things first...... Get a tach and a way to measure GPS speed. You need to know where you are at so you can tell if the changes your making are improving your situation or not. You also might find that your not up to the 6800-6900 rpm and above 55mph performance that you should be seeing.
 
No, the stock speedo is very unreliable and usually reads high. That is why they have been called the Dream-o-Meter.
 
Ahh I see any part numbers for me? I’ll take your guys words on speedos. I saw a few on eBay that were stock style but I’ve never used a gps speedo
 
No but it was the first power valved and counter balanced engine in the skis. I am pretty sure the basic design came from their snowmobiles.

The 720 made 85 HP and the 787 made 110 HP so there was a pretty big jump without much of an increase in size. The next up wat the 951 that made 130HP and then the RXX 951 that made 160HP. Those were pretty high strung since Kawasaki, Yamaha and Polaris all went over 1,200cc and triple cylinders to get those kind of numbers. That was the end for the 2-strokes.
 
Just to put this out there, the reason ethanol is a poor choice for PWC’s is twofold.

First, ethanol is hygroscopic, so it tends to absorb moisture (water) from the air. Since we operate in damp, humid air exclusively, the ethanol will pull water into your fuel system.

Second, the stoichiometric ratio of ethanol is 9:1 rather than the 14.7:1 that all of us hot-rodders are used to. This means that if a carb is jetted properly for 100% gasoline, that carb will be set WAY too lean for ethanol. That’s why in the car wold you see the guys running E85 using massive injectors. It just takes more fuel to do the same amount of work.

Sorry if I took the thread off on a tangent, I just thought it might be helpful for some to have a little background on the alcohol issue.
 
JeremyD615 said:
Just to put this out there, the reason ethanol is a poor choice for PWC’s is twofold.

First, ethanol is hygroscopic, so it tends to absorb moisture (water) from the air. Since we operate in damp, humid air exclusively, the ethanol will pull water into your fuel system.

Second, the stoichiometric ratio of ethanol is 9:1 rather than the 14.7:1 that all of us hot-rodders are used to. This means that if a carb is jetted properly for 100% gasoline, that carb will be set WAY too lean for ethanol. That’s why in the car wold you see the guys running E85 using massive injectors. It just takes more fuel to do the same amount of work.

Sorry if I took the thread off on a tangent, I just thought it might be helpful for some to have a little background on the alcohol issue.
Click to expand...

Great information!. The last thing you want is an even leaner mixture in a 2-stroke.
 
Makes sense. I’ve heard guys say that absorbing water wasn’t that big of an issue but he was talking about street cars. Not skis. The big reason hot riders like E85 is the boost and you can run more timing and more compression.

With this 787xp ski I plan on replacing the impeller with something new and something that will net me a gain in both acceleration and top speed. This is a stock prop mind you so what is a good idea as far as an impeller?

After that discussion my drawing board consists of
1. Tach and speedo
2. Impeller because the one in it is shot
3. I’m thinking rossier pipe
4. At least a rejet of the carbs, will this be enough or should I look at getting some bigger carbs too?

Is the gray box tuning worth doing before mods or should I wait until after I get some work done.

Also are you guys running 91 or 93 octane?
 
I always run fresh 93. Seadoo did a great job with the impeller and the rest of the tuning for that matter so it's hard to beat. A Skat swirl will pull harder and a Solas XO will have a little top speed advantage. Keep an eye open on the market and ask here before you buy.

I'd sell you a Factory Pipe Spec 1 with the appropriate carb and water jets and a good impeller for $500 shipped so let that be your baseline.
 
The car guys love E85 because it’s got an octane equivalence of about 108, and it’s not $40/gallon like C16 is... The power comes from the increase in timing and compression though, not the octane rating itself. The most power any given engine will make is with the lowest octane fuel that will run detonation free. If you were to run the same engine, under the same conditions, with both 85 octane and 93 octane, and there was no knock in either case, the dyno result for the lower octane gas would actually be higher by 2-3% in most cases. Of course in the real world, you would advance the timing on the higher octane run to more than make up for the difference.

A ski works the same way, and if you could keep moisture out of your fuel system, E85 would be great for a high compression, milled head Rotax motor. Unfortunately we are dealing with extremely small orifices in our carbs, and moisture in the fuel system can actually be enough to prevent fuel from passing through them. That can lead to an instant lean condition, which is a death sentence for a two stroke.

As far as your impeller goes, I would have the factory unit refurbished and a new OEM wear ring installed before I made a decision on an aftermarket one. It sounds like you’re looking for balance between speed and acceleration, and the factory pitch is pretty well suited for that. To move the needle towards top end speed, you’re generally going to give up holeshot and vice versa. Of course if you’re adding a pipe and rejetting carbs, you may pick up enough horsepower to make it worthwhile to repitch that impeller...
 
500$ shipped sounds pretty good I’ll definitely use that as my baseline. I’m excited for the season that’s for sure. I have to run up north to get the ski so I can compression check it and replace some fuel lines but that should be within 2 weeks..... then I can start doing the fun stuff.

Thanks for the rundown on E85 by the way I like the added compression but it’s not worth it on the water. I’ll burn 93 for my 2 strokes
 
CantSWIMbutSEAdoo said:
500$ shipped sounds pretty good I’ll definitely use that as my baseline. I’m excited for the season that’s for sure. I have to run up north to get the ski so I can compression check it and replace some fuel lines but that should be within 2 weeks..... then I can start doing the fun stuff.

Thanks for the rundown on E85 by the way I like the added compression but it’s not worth it on the water. I’ll burn 93 for my 2 strokes
Click to expand...

if you are replacing the fuel lines I would check the carbs too!
1553126355070-png.39602
 
CantSWIMbutSEAdoo said:
500$ shipped sounds pretty good I’ll definitely use that as my baseline. I’m excited for the season that’s for sure. I have to run up north to get the ski so I can compression check it and replace some fuel lines but that should be within 2 weeks..... then I can start doing the fun stuff.

Thanks for the rundown on E85 by the way I like the added compression but it’s not worth it on the water. I’ll burn 93 for my 2 strokes
Click to expand...

Anytime! I’m still not a PWC expert by any stretch of the imagination, but I’m a gearhead, and I did own a company that developed processing equipment for the alternative fuel industry back in the early 2000’s, so I’ve done quite a bit of research on that particular topic...
 
Gents. I nabbed the xp from the cabin..... brought her home and did some power washing replaced the plugs and had to get a battery but she lives! Now I have to put it in the water and check for leaks, tune carbs, some buffing and possibly an impeller. Hopefully I can keep it alive for the summer. My next project is an gsx with a 787 that needs a top end. Ski was free though so all I’ll have into the sxp will be another battery and a couple pistons.
When I get to some WiFi I’ll try and post some pics..... having trouble doing it at the warehouse
 
It looks like yours was in similar shape to the way I got mine. It’ll clean up good with a little elbow grease and a good buff ‘n polish...
 
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