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  1. #1
    gordon lasiter #328's Avatar
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    What is a safe AFR?

    i went from a c3 wheel to a c5 wheel, with a 12.5 afr this is what happened to the #2 piston.Click image for larger version. 

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    i will be getting the injectors flow tested to see if that was the culprit.Click image for larger version. 

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    but, with a c5 wheel, i am thinking the afr should be around 12.0

    i am getting the riva internal upgrades and plan on running a perminent afr gauge.Click image for larger version. 

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  2. #2
    Hows your ski setup? RPM? RRFPR? mods? Injector size? Etc.

  3. #3
    Idle = 12.5
    2000rpm = 12.8
    2500rpm = 13.5
    3000 to 4000rpm = 14.0
    4000 to 5000rpm = 13.8
    5000 to 5500rpm = 13.7
    6000 to 6500rpm = 13.4
    6500 to 7000rpm = 13.2
    7000rpm = 12.7
    7500rpm = 12.3
    8000rpm = 12.1
    WOT = 11.8

  4. #4
    desperado's Avatar
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    Sorry to see you lost your engine. Your question need to take into account other variables such as ignition timing advance, fuel octane used, engine temperature, spark plug heat range, injector flow volume and fuel pressure stability on sustained WOT operation. That being said, 12.5 AFR does not leave much safety margin on a ski with a C5. The risk to go bang increases significantly whenever one of these variables is not setup right for your ski. This is why many people choose to go 11.8 to 12.1 AFR with some additional fuel compensation going to #2 and #3 cylinders -- it allows for a greater safety margin whenever something goes south with fuel quality, fuel pump pressure, engine temperature, timing, etc, etc, etc....

  5. #5
    gordon lasiter #328's Avatar
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    Quote Originally Posted by gashog301 View Post
    Hows your ski setup? RPM? RRFPR? mods? Injector size? Etc.
    with the c5 i did not get to see what my rpms where before it starting to act up.
    but,last time i rode it before changing the wheel and the ecu reflash:
    with a c3 wheel,jd intercooler, rfrpr 52 lbs @ static, r2 reflash,14/23 skat with a 85mm nozzle ring, freeflow exhaust with a riva waterbox.
    my rpms where 8400 to 8500 depending on the water i was riding in.
    i would race in 100 mile enduros that consisted of (2) 50 mile motos.

    with the new setup i added the c5,r3 reflash,rrfpr set @ 52 lbs. rising rate. 2nd thermostat, the afr was reading 12.5 when the cylinder failed.

    other items added that should not effect the afr are: billet coupler,lightened and balanced idler gear. twin prop.

  6. #6
    SHOBiz's Avatar
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    Quote Originally Posted by gashog301 View Post
    Idle = 12.5
    2000rpm = 12.8
    2500rpm = 13.5
    3000 to 4000rpm = 14.0
    4000 to 5000rpm = 13.8
    5000 to 5500rpm = 13.7
    6000 to 6500rpm = 13.4
    6500 to 7000rpm = 13.2
    7000rpm = 12.7
    7500rpm = 12.3
    8000rpm = 12.1
    WOT = 11.8
    Similar to mine, but a tad richer on the bottom

  7. #7
    Addicted Member 5001craig's Avatar
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    How long had the gas been in the ski?

    The thread started about gas by Tommy Jordan has really made me think.

  8. #8

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    Was the head gasket leaking?
    Is the oiler under the piston still operational?

  9. #9
    gordon lasiter #328's Avatar
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    Quote Originally Posted by 5001craig View Post
    How long had the gas been in the ski?

    The thread started about gas by Tommy Jordan has really made me think.
    the fuel was topped of the last time i rode it before winter which was in mid november.
    i rode it in feb. when it was not running right. it had "popping" sounds coming from the exhaust when trying to give it throttle. looking back know that was probably detonation aka "knocking".
    the cylinder actually gave out in april when it had the same fuel in it that was from november.
    i usually use stabil in the fuel, but i did not use it last winter.
    it was odd because at times it would run good then, it would run like crap.
    that is why i am thinking it might have a clogged/dirty injector.

  10. #10

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    I may be missing something, but, you may be too lean in the 5000 to 7000 rpm range. The overall a/f is an average of all cylinders, you could easily be 5-10% leaner on an individual cylinder. The problem can also be compounded by uneven cylinder cooling. On a boosted engine keeping the a/f at 11.5 to 12.0 at any wot rpm is more desirable from a reliability standpoint. You can be at 15:1 all day if you are at no load.

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