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  1. #1
    SURFnTURF's Avatar
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    Coffman pipe exposed

    This pipe has been sitting on a shelf for 2 years and thought I would install it on one of our xpls (ex race boat) So installed it all good and micro touch limiter then off to the water for testing. All good has great low down power but no top end ,will only rev to 6250rpm. Leaned the carbs a little with no better results, removed pipe from ski and pressure tested pipe and found it held zero pressure.

    Hooked hose up to it and could hear water pouring through into the chamber. Well normally guys throw these away with this problem but these are hard to come by so I went a cutting.

    Filled the pipe totally up with water and I could isolate how high the leak was inside the pipe and then rotated it until I could hear water squirting again.That told me which side so I cut and found a split approx 2in long as per the picture.Will pressure test inside of pipe now and then weld the outer skin on now and hopefully should be all good.

    Just thought I would post a picture so guys can see how the water jackets work on a Coffman.
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  2. #2
    96XPSS's Avatar
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  3. #3
    PEST!'s Avatar
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    Thanks for the pics. I think you need to grind down the patch a bit before the skin will fit back on.

  4. #4
    jetskibum1's Avatar
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    Jetting

    Quote Originally Posted by SURFnTURF View Post
    This pipe has been sitting on a shelf for 2 years and thought I would install it on one of our xpls (ex race boat) So installed it all good and micro touch limiter then off to the water for testing. All good has great low down power but no top end ,will only rev to 6250rpm. Leaned the carbs a little with no better results, removed pipe from ski and pressure tested pipe and found it held zero pressure.

    Hooked hose up to it and could hear water pouring through into the chamber. Well normally guys throw these away with this problem but these are hard to come by so I went a cutting.

    Filled the pipe totally up with water and I could isolate how high the leak was inside the pipe and then rotated it until I could hear water squirting again.That told me which side so I cut and found a split approx 2in long as per the picture.Will pressure test inside of pipe now and then weld the outer skin on now and hopefully should be all good.

    Just thought I would post a picture so guys can see how the water jackets work on a Coffman.
    Aside from your pipe issue, would you mind sharing your jetting specs and what jets you ran to your mid pipe, stinger and waterbox. I am playing with one of these pipes now on a 99 xpl with microtouch also.

    Cheers.

  5. #5
    SURFnTURF's Avatar
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    Quote Originally Posted by jetskibum1 View Post
    Aside from your pipe issue, would you mind sharing your jetting specs and what jets you ran to your mid pipe, stinger and waterbox. I am playing with one of these pipes now on a 99 xpl with microtouch also.

    Cheers.
    Pest: yes it will have to be so I can get it back on and not create a hot spot where water cant get to.

    My set up:
    No pumps on carbs used. Highs 170 adjuster open 1/2 turn (then tune), lows 95 open 1.75 turns (then tune) 2.3 N/S with 95 gram spring (pop off 19-21 psi )
    I usually don't set the Coffman pipe up with water injection because they usually rev so quick through the rev range the benefits are not noticeable.Quite different to a stock pipe.The stinger requires a 125 jet into the barb fitting this will keep the couplers cool enough even on long WOT runs.
    The water box you remove the water control valve and brass insert and install a brass plug so no extra water is required.You will have to block off the water control valve water hose which will still be under pump pressure.

    The micro touch I remove all the jumpers which gives max retard rate and max rev limit.
    These have to rev into the 7300 to get max power so re pitching props is required if you dont achieve those revs.
    If it seems to rev ok but about 7000-7100 the acceleration rate drops then it gets over that hump your prop is too tall.You cant have these pipes stalling through the rev range as it will detonate the engine,it should from idle in the water rev straight up to 7300 without hesitation.If not change prop pitch(very important as this is why they got the name purple piston eater) because they build too much heat at 7000-7100 while being over propped.

  6. #6
    jetskibum1's Avatar
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    Awesome help

    Cheers for that, I will keep my eyes on those rpms

  7. #7
    SURFnTURF's Avatar
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    Thought I would post up another image cause we found another leak at the mid pipe area so cut cut cut.All fixed now revs into the 7400 with no hesitation from idle.
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