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  1. #1

    Second outing on STX12-F & 15-F ** Update

    After changing the plugs on both and repairing the exhaust/water box hose on the 15, we went out again yesterday.

    The good news- both machine ran well and we were able to ride for for as long as we wanted. The 15F is a beast for a stock ski. I'm very happy with performance and other than the display being crap and a taking on a small amount of water while not running, I'd say this ski is well sorted.

    The 12F is a different story. I had a hell of a time starting the ski. Once it starts it runs and restarts fine but if it sits for more than 30 minutes, it's a bear to start . Once running, it still won't go over 46MPH or 6000 RPM. It just doesn't "feel" strong. I suspect the impeller may be damaged because I think I see a lot of air bubbles in the jet stream? I put in some octane boost and fuel injection cleaner and plan on tearing down the the pump to check the impeller.

    Any thoughts on the hard starting? It almost seems like a fuel pressure issue... is there a check valve on the pump to maintain fuel rail pressure?
    Last edited by JAV; 08-26-2012 at 08:36 PM.


  2. #2
    Check the cyl compression on the 12F before anything else.

  3. #3
    I tried to do that when i changed the plugs and found my compression tester didn't have the right 10mm adapter. I ordered it today.

  4. #4
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    While you are waiting for the adapter pull the pump and check it out, it can't hurt.

    Sean

  5. #5
    yeah- I'm hoping it's the pump...I hadn't allowed myself to consider catastrophic engine failure with 126 hours.

  6. #6
    Well- it seems sunday is the only day I can spare any time to work and ride the ski's. I got my compression adapter and went to warm up the 12 to run a compression test. Of course the thing is having a real hard time starting so I decide to test fuel pressure. Yep- 25 psi while cranking...Houston- we have a problem.

    Off comes the fuel pump and I get it stripped down to the bare components. Sure enough the regulator is leaking pressure. With no parts stores open, i decided to try some things I've done on cars. After dis-assembling the regulator, i cleaned out all the pieces, ran some wd-40 through it, blew it out good and pressure tested it. No more leak but it was still releasing at under 30 PSI. So I jury rigged a press jig and compressed the spring cap about .025". Pressure tested again- got to 37 psi. Compressed the spring cap another .030 and it pressure tested at 45 psi. Assembled it back into the ski and Voila- started right up- with 45 PSI while idling.

    Took the skis out for a run in the ocean and now the 12 goes past 7000 RPM and clocked at 57 MPH in some decent chop (true 1-2 footers). It actually "feels" right- not quite 15F strong- but it's no slouch now. The only remaining issue is it likes to stall if you let off the throttle abruptly when slowing down. if you gradually let off, it stays running but if you release it all at once, it stalls more times than not. Does anyone know if the EFI system is adaptive? Could the fuel pressure being 2 PSI above stock be contributing to the stalling?

    The 15 again ran VERY strong.... that is until we almost sank it. Last week, we noticed a good amount of water drained out of the drains when we trailered it and popped the plugs on the ramp. This time, we put it in the water and checked for leaks. We found none. I had the kids take the skis out into the bay then I met them out there with our boat. Again, I checked the 15 and there was no appreciable water in the biige. We took turns riding both for the after noon and eventually tied both skis to the boat and had some snacks. When we were going to leave, my son was on the 15 and I was on the boat and he immediately noticed the ski didn't feel right. Long story short, the hull was half full of water. It was all he could do to get it back to the ramp and once on the trailer- it took close to 10 minutes to drain. I estimated 40-60 gallons of water in the bilge... maybe more.

    Once home- we found a split hose while flushing the engine.. how we missed it before- I not Know! I'm just glad we found it! Looks like I have another project for next sunday- new hose AND auto bilge pump! Has anyone ever cut a bigger hole over the drive shaft to fit in a bilge pump?.

  7. #7
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Re: Second outing on STX12-F & 15-F ** Update

    I'm running mine where the secondary water box used to live.

    Glad you got the 12 working. The ski is a dumb ecu and can't tell if you changed anything. I'll bet that its the idle control valve over the throttle body that is causing the stalling. Do you hear a clicking sound when the ski engine is turned off?

    Sean

  8. #8
    Yes- I hear the clicking. It's funny you mention that... I didn't know what it was BUT when i had the fuel pressure gauge on the rail, that clicking dumped all the fuel pressure from the rail before I tweaked the regulator. Once I fixed the regulator, the clicking reduces the fuel pressure to about 30PSI but some rail pressure is maintained. The starts right up now.

    I have no idea how it's supposed to work but I did notice while flushing that the idle was fluctuating more than it had on the water... to the point of stalling. Is there a way I can check it?

  9. #9
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Re: Second outing on STX12-F & 15-F ** Update

    The 12 and 15 use the same part so swap them and check

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