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  1. #21
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    Quote Originally Posted by Mr Noisy View Post

    Regards a tach, and running total loss, I run a regular ignition coil, a dynacoil DC-1 as it happens
    Would it be suitable to pickup the tacho signal from coil negative as per a regular auto tach?

    For our purposes it would be better to use an inductive pick-up style, like the PET.
    There are a few other PET tachs that are real high quality.

    For now the goal is to estimate where the engine makes peak HP, and confirm
    that it is, or isn't producing our rpm goal.


    Bill M.
    Last edited by wmazz; 07-19-2014 at 05:48 PM.
    Horsepower == Speed, RPM != Speed



  2. #22
    I dream skis Mr Noisy's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    Ok bill, great stuff, will get back to you tomorrow, thanks a bunch!

  3. #23
    I dream skis Mr Noisy's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    Hi guys

    Ok so today (I'm 8 hours ahead of LA time!) I will get some pics and measurements of this motor

    This is the tacho I am planning to buy, they are readily available here in UK and come with good reviews

    Hope y'all approve

    http://www.tinytach.com/commercial.php

  4. #24
    I dream skis Mr Noisy's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    Bill,

    I've been reading some more of your posts around on the forum regards impeller choice.

    I now understand more about the importance of correct choice, because of the peak rpm requirement which, I assume, is all down to this port timing?

    I read a post you made about an engine seizing due to detonation if run at WOT short of the rpm peak, it is fair to say the racing cylinder I have fitted may require a higher rpm than my pump can make, especially as you say with a stock nozzle.

    It's all kind of slotting into place now.

    The cylinder that has failed has some pitting around the top of the bore which looks like it may be due to detonation, I'm rather certain it wasn't there before.

    I will get some pics but it is above the ring sweep area so im thinking I will be able to run the cylinder despite the damage.

    Also, ignition timing is an unknown for me so I hope it is something we can discuss.

    I have a DTI if it will be necessary!

    Thanks

  5. #25
    Top Dog Goong Gang's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    Use a Keihin 42mm Sudco instead.
    If it's worth doing, it's worth over doing!!

  6. #26
    I dream skis Mr Noisy's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    I particularly would like to make these BN38 duals work nicely

    It will be possible

    I'd like to keep the ski vintage and old race skis would have tended to have dual 38s I guess

    I'm a sucker for old school!

  7. #27
    I dream skis Mr Noisy's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    Hello everyone!

    I have plenty of pics and info Bill.

    I must say I am so grateful for you taking the time to look at this situation for me, otherwise id be really struggling!

    I got some shots of the pistons etc at both crank phases, the rear is on the left:





    Front:



    Rear, you can see the bore damage here:



    Then I took the piston crown to deck height, it wasn't easy because of the small measurement and the piston crown did not give a level surface:



    Front 0.84mm
    Rear 0.94mm

    And then BDC to deck:



    Front 70.84mm
    Rear 70.82mm

    And then top of exhaust port opening to deck:



    Front 38.20mm
    Rear 37.80mm

    Then I took the centre transfer port to deck, these have been angled upwards quite a lot I think:



    Both front and rear were around 57.00mm to deck, all ports are approx level.

    Next, I took a couple of pics of the pitting on the rear cylinder, although now I think it may just be corrosion???

    Only thing is I'm not sure I had seen it before.





    And then finally I checked out the impeller, it's a Skat 7:



    Really hope you can make something of that lot Bill, I owe you a beer!

  8. #28
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    I don't have enough time to give a full answer now, and there is plenty
    to talk about. Your exhaust timing is close to 190 degrees of duration.
    It looks as though you have had a history of blown head gaskets, and
    the impeller appears to be a 17 degree straight pitch. If I am correct,
    that is a real bad combination, and it would seize no matter what
    carburetion was used.

    Note: Anyone, if you can identify that impeller as something other
    than a 17 degree impeller, please speak up. Other possibilities are a
    14/17, or a 9/17.



    Bill M.
    Horsepower == Speed, RPM != Speed



  9. #29
    I dream skis Mr Noisy's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    That's ok bill, no rush.

    The head gasket has warped and there is evidence of blowing or at least very hot spots in the gasket around the bore.

    After some research, I'm quite certain it's a straight 17 impeller.

    The cylinder was from a westcoast works racing ski, hence it's wild setup perhaps.

    I look forward to your thoughts, somewhat apprehensively!

  10. #30
    I dream skis Mr Noisy's Avatar
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    Re: Trying to setup dual 38 carbs for very hot 650 X2!

    Also, I have just found a straight 15 impeller in my stores.

    Do you think that will work for me?

    These old props are hard to get hold of, otherwise I'd love an 8/16!

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