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  1. #1

    XL1200 ltd free flow exhaust worth it ?? Also looking for reliability mod ideas.

    Looking into a few things for my ski and came accross a mod "free flow exhaust" was wondering if it would be worth it to put on the ski. I have R&d ride plate and the 800 grate, D plate and chip, WFO carb jetting, pre mix, primer kit, filters instead of air box, wave eater clips, fuel pick up flap removed, jetted fuel return. Basically stock so am looking to make it as reliable as possible as it is a family ski.

    So any benefit to the free flow or just not worth the money. I read somewhere that the hose from 99 or 98 1200 will work as well but can't remember for sure.

    How about the pump stuffer kit .....needed or ? Worth the money ?

    let me know your opinions guys and also anything else I should do to keep this thing as reliable as possible.

    Thanks


  2. #2
    Prism's Avatar
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    The free flow's main purpose is to quickly rid the waterbox of excess water when the throttle is punched. The good news is, this increases throttle response and "holeshot" slightly. The bad news is it makes the ski louder and actually decreases peak rpm and top speed slightly. 4 stroke exhaust theory is much different than 2 stroke theory and relies on a return sonic wave back to each cylinder to prevent over scavenging of the fuel and air charge. This is why there is a decrease in peak rpm as that sonic pulse is weaker with the free flow. (More of that wave travels out the exhaust) On highly modified engines with a lot of porting and compression, it can help stop detonation from a reduction of this reflected sonic wave. This lets more of the intake charge flow through each cylinder in the form of increased cylinder scavenging taking combustion heat with it. This reduces cylinder temperature and keeps detonation at bay. On stock and lightly modified engines, this is not needed or desireable as the combustion chamber remains cool enough to not pre ignite or detonate.

    The pump plug kit fills the casting voids in the pump shoe and is installed when sealing the pump shoe to the hull. High horsepower, heavy ski weight or towing can induce "prop slip" or cavitation. This feels like a car spinning it's wheels on snow. Lots of engine noise but the ski doesn't accelerate strongly from a stop. When water flows over an uneven surface under a vacuum, it causes air bubbles to form from the water actually boiling at low temperature. These air bubbles can compress in the pump and lead to a loss or severe reduction in propulsion. Repeated operation with severe cavitation can result in prop and pump vein errosion. If you're ski is not cavitating now from a stop, you will not see much difference from installing a pump plug kit and sealing the pump shoe. If you are cavitating now, it might be worth it...just make sure there is nothing else inducing the cavitation.

    You already have the d-plate, wave eater clips, premix, and flapper removed. If WFO modified and installed your carbs, all is good! Sounds like you have addressed many of the common issues with a carbureted Yamaha ski. The only thing I'll add, is make good use of Sta-bil fuel stabilizer and keep your tanks full at the end of the season. Good luck with it....now go out and have some fun with the family!
    Last edited by Prism; 05-31-2015 at 03:09 AM.

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  4. #3
    Prism,

    Thanks very much that was an awesome explanation. Exactly what I was looking for.

    Few more parts left to install then hope to out on the water next weekend.

  5. #4

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    One other thing that helps with power pretty much everywhere is more compression, milling the head. Requires the use of 91-92 octane though, but does not require any other changes. You do not need to change the jets either.

  6. #5
    Protec intake manifold ?? Worth it or not for this ski ? I can get one for about $100

    let me know
    thanks

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