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  1. #1
    EJRex's Avatar
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    98 GSX-L R&D Power Plenum and 49cc Head Questions..

    I've got a red deck/silver engine gsx-l.. Bought the ski used, so far as I know as it sits now: stock grate, stock ride plate, stock prop, aftermarket single air filters (dunno the brand), stock carbs, stock exhaust, umi race bars.

    I wanted to get a little more mid and topend out of it and was considering the R&D power plenum and maybe a 49cc rec head. Didn't know if I need a rejet or anything to compliment this setup. I'm also not dead set on these items. I've looked at the solas concord 15/21 prop and pump wedge also. I don't want to get into the motor if I don't have to.. I'm new to the 951s, so any help is appreciated.


  2. #2
    rhyne717xp's Avatar
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    If you already have aftermarket flame arrestors, I wouldn't get a R&D power plenum. If yours are the single type then they are more than likely prok/Fly Flame arrestors which are better IMO. I believe upping the compression will give you better low end power and some mid. To get more top end an impellar would give you that. To get more Rpms you would have to do a pipe and or water injection system/rev limiter. Doing a pipe will breed a whole lot of tuning. Pipes eat pistons if not perfectly tuned. I would get an impellar that is rated for your stock engine and be done with it. If you go too high on pitch you will deto a piston. Believe me I have done it lmao!!! Hope this helps ya bud.

  3. #3
    silver motor with white pipe - open flame arrestors with atleast 85 lows and 165 highs - repitched prop to bring max rpm's up to 7000 - on an otherwise stock boat

    And since this is a used, but new boat to you, remove and clean the carbs.. Dirty carbs are the number one cause for most of the issues and failures on these boats..

    Mikuni Carb Rebuild Kits are highly suggeted

  4. #4
    EJRex's Avatar
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    Carbs have been thoroughly cleaned, that was one of the first things done when I bought it, along with new fuel/oil lines. I've been looking around for a white pipe, but they are not easy to find so far.. according to the tach (I know they can be off) I usually hit 6950-7050 rpm at wot.. there may be more done to the ski than I know so far, but I will find out. For the moment, the pipes and head are stock so I will start there and leave the filters alone. Will look into those jets as well, if they're not already in it. Thanks for the replies guys.

    Also, where is a good place to get a repitched prop?

  5. #5
    I beleive a lot of people use - http://impros.com - to get their prop repitched..

    When I bought my boats, one turned 6950-7050 and the other turned 6850 - I will tell you that these boat will run mean, when they run lean - since somebody swap the arrestor on mine and never rejetted it - it ran great til it melted the rear piston.. There are many factors that effect jetting and not saying you may have an issue with yours, just saying.. But you really want to jet, not for the highest rpm (as that is a lean mixture) but rather the highest rpm minus 100-200 rpm (as you go richer you will see a lose of engine rpm's) and then repitch accordingly..

    The stock rev limiter is set for 7200 rpm +-50 rpm and seadoo usually leave a 200 rpm cushion, so 6950 rpm is about right..

  6. #6
    DPG98GSXL's Avatar
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    Having my 98GSXL since it was new and the only owner of this fast, nimble little craft. I have had a lot of fast and fun times and even went thru a over detonation time with the engine. When you start pushing 7k RPMs, you are on that edge of "BOOM". I have a safe set up "I feel" and it is dependable!!!! I am out to ride and have a good time. It is very fast, arm wrenching out of the hole and lost no top end.
    My current RPM's are around 6700-6850 depending on humidity.

    My current set up is:
    Prok flame arrestors "More Air"
    Beach House Sponsons " more stability"
    Worx Top Loader water intake grate
    Level 1 rejected carbs PPG (running a little rich)
    Primer kit
    Solas concord swirl 15/20. "WOW"


    With this set up, my ski is "SMOKE ON THE WATER". Great CC racer...
    Last edited by DPG98GSXL; 01-06-2013 at 02:25 PM.

  7. #7
    EJRex's Avatar
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    Good info, thanks for the link. I wasn't going to add a grate or aftermarket sponsons cause they can rob mph, but I have looked into the concord prop.. also looking at a ADA 50cc head, but I can't seem to find a white pipe anywhere, unless it's just the cone. I don't have enough posts on here yet to buy anything, so gotta fix that

    Does anyone still make an exhaust pipe for the 98s? And has anyone ever had their MPEM programmed?

  8. #8
    DPG98GSXL's Avatar
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    Quote Originally Posted by EJRex View Post
    Good info, thanks for the link. I wasn't going to add a grate or aftermarket sponsons cause they can rob mph, but I have looked into the concord prop.. also looking at a ADA 50cc head, but I can't seem to find a white pipe anywhere, unless it's just the cone. I don't have enough posts on here yet to buy anything, so gotta fix that

    Does anyone still make an exhaust pipe for the 98s? And has anyone ever had their MPEM programmed?
    I beg to differ on the sponsons>>>>IMO, the sponsons are a big factor... it added stability and would plane out faster out of the hole and would allow to get to the top end faster...
    On the grate>>> the top loader will fill the faster pitched prop... Remember, it's a bigger pump and can handle the extra water...
    On the pipe>> I have heard the Coffman pipe is good on the 951's... I still have he stock black pipe...

  9. #9
    EJRex's Avatar
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    Quote Originally Posted by DPG98GSXL View Post
    I beg to differ on the sponsons>>>>IMO, the sponsons are a big factor... it added stability and would plane out faster out of the hole and would allow to get to the top end faster...
    On the grate>>> the top loader will fill the faster pitched prop... Remember, it's a bigger pump and can handle the extra water...
    On the pipe>> I have heard the Coffman pipe is good on the 951's... I still have he stock black pipe...
    Oh I'm not arguing that grates and sponsons don't make a huge difference, only that they create drag and can slow you down a bit. I checked out the coffman pipe.. 969$ I'll wait for a white pipe!

  10. #10
    DPG98GSXL's Avatar
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    No problem..

    The drag is not there with the BH sponsons.... I assure you.

    DG

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