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  1. #1

    STX-12F with a few minor upgrades

    Hi all, First post on this forum but I've had a few ski's over the last 20 years. I have a 2005 12F that was recently given to me by my boss before he passed away. Right now the head is off because of a broken spark plug, and I'm cleaning everything up before reassembly. I have a few minor mods that I'm working with while it's apart.

    I've removed the second water box per the R&D instructions, and modified the first box. I'm making my own air box mod (copied from the setup I've seen on this forum, with air filter mounted in the rear storage container. I'm also considering the timing plate mod and there are a few choices out there. The obvious one to me is the ADA Racing plate, it's only $69 vs the TBM cover which is $200. I'm having a hard time finding more than one place that carries a 2 degree wedge for the pump. Also, can't seem to find anyone with a Shredmaster plate, are they discontinued?

    Stock this ski usually peaks at 55-56 according to the speedo. I'd like to get the nose up a little bit and maybe it won't be so bumpy. At low speeds it submarines and plows through the water, at high speeds it seems to suck itself down into every little wave, much stiffer ride than I expected from a big 3 seater. I'd be happy if it would do at least 60. (my last ski was an SL1050 2 seater Polaris, almost 70 mph...got me hooked on quick skis).

    Anyways, I've been using the search and reading through the forum for a few weeks. I was just wondering what anyone thought of my few little mods, if there's something better. Also if someone's got a source for that 2 degree wedge, I'd appreciate it. I've seen some people say with that wedge you need a ride plate or else it gets a little out of control at high speeds. I am planning on a plate, impeller, and intake grate replacement at some point. I'm not a fan of the top loader plates that hook up but kill the top speed, I'd rather keep the stock or modify the stock.


  2. #2
    785xp's Avatar
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    You can also look at the R&D ride plate if you can't find the Shredmaster. If I remember correctly, no one found any real advantage to running the pump wedge. Since you are working on the airbox, would you mind letting me know what the diameter of the throttlebody is? I am looking to get a 15F this winter and will need to know what size cone I need to order since it will probably be left in storage. I was going to do something like this:

    http://www.pwctoday.com/showthread.php?t=269700

  3. #3
    I've read more than a few people with the same complaint as me, that the nose sits too deep in the water when only one person is riding. They all claim to have gained about 2-3 mph by getting the ski out of the water a little. Makes sense, I'll find out for myself though if I ever find a wedge that fits.

    The TB has a 2.75" inlet. I bought a universal Spectre filter ($25) identical to the one in your link (except I chose the white one). Then I bought (for $9.99) the 3" diam universal tubing, and a 90 degree elbow to turn in to the airbox/storage box. I also got a 3" to 2 1/2" rubber coupler that fits right over the throttle body and the straight pipe. It should have a nice deep sound to it during acceleration, echoing in that storage box.

    From what I've read, with the air filter mod, one guy noticed a huge gain in off the line acceleration. He said he wasn't sure about top speed gain, but torque off the line was much stronger. IMO, it looks nicer anyways, and if I don't like it, not hard to reinstall the old box/anchor.

  4. #4
    Pain is fear leaving your body.... rlovebk's Avatar
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    You can spend a bit of $ and gains only 4-5 mph. Shred is best plate but hard to find and spendy. Wedge will get you small gain but cost you on rough water hook-up and handling/tracking. Careful with the timing they like to go lean and detonate due to higher compression.
    12F gains (55mph to 60) vs. coin spent roughly same as 15F, (60 mph to 65).
    Anti-seize on plugs always and torque always.
    Enjoy and good luck. Great little ski.

  5. #5
    785xp's Avatar
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    So the throttle body has needs a 3" inside diameter filter or cone to fit? Do you have a link to the modification you are doing?

  6. #6
    The TB is about 2.75" but I think a 3" will still tighten down. This is what it's going to look like when done....http://www.greenhulk.net/forums/show...997#post500997

  7. #7
    UPDATE: I've gotten it almost all back together, enough to start and know that it runs again. For the timing mod, I decided to spend $0 and modify the stock plate that's mounted on the crankshaft/sensor. This is the link to the instructions I used, was the easiest cheapest mod I've done so far....and what a rediculous major improvement in throttle response that little bit of timing really did- http://www.greenhulk.net/forums/show...r+modification

    Also, got the air filter "Bucket" mod complete, looks great, works great. Instead of hot air from behind the engine and muffler area, the engine now breathes cool outside fresh air. Instead of the restrictive air box, it has a big cleanable cone filter. Looks great, sounds great, and supposedly an improvement in low to midrange power band.

    I cut open the exhaust and did this exhaust mod http://www.rivaracing.com/instructions/rk16085.pdf. I still need to find the Riva water outlet fitting and replacement brass water box fitting since I don't have the kit. Besides that, I cut open the muffler, removed the block off plate, welded the muffler back together, and removed the secondary water box. It's got a nasty rap to the exhaust now when you hit the throttle, sounds like a real 1200 engine finally.

    I also got a hole saw kit and opened some of the air inlets to get fresh air through the hull. I opened a 3" hole forward of the instrument panel, behind the storage compartment. Also opened 2 holes 2" each in the rear seat bracket that allows fresh air to get to the vent hoses for the air filter bucket mod.

  8. #8
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Re: STX-12F with a few minor upgrades

    Since you added timing don't run less than 93 octane to be safe.

    Sean

  9. #9
    Actually I was afraid of even running 93, especially 10% ethanol. I try to only run 100 octane avgas. There are times that I need to fuel up during the day and can't run back to my hangar for more fuel, then I'll add plenty of octane boost. This ski only has 39 hours on it since 2005 when new, but has only had 100 LL avgas about 38 of those hours.

    Thanks for all your previous posts of your mods, that gave me an excellent guideline. I'm copying your version of the second water box removal as we speak. I'm trying to figure out how to fit that U-pipe in place. It's a tight fit. Mine is a stainless steel pipe with 8" center to center from the bend (4" radius?).

  10. #10
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Re: STX-12F with a few minor upgrades

    I have 75+ hours on my 6 degree advance with 93 octane and no ill effects so I wouldn't worry about it, you have to remember that the ski was designed to run on 87 with 10% ethanol. It's a bit of a pain to get the u bend in. I found fitting the hoses to the u bend with the 2 hoses then fitting everything was easier than leaving them connected and fitting the bend in the hull.

    Sean

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