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  1. #1
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    Sep 2007
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    Kansas
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    Default YZ 125 compression questions, race fuel, pump fuel

    Just rebuilt the top end on my 125 with a fresh piston and ring, and a cometic thin base gasket.

    What is the stock compression?
    What is the max compression that can be run with pump fuel?
    When do i have to run race fuel?
    What is too much compression for a 125?

    I havnt checked the compression yet but it seems pretty high and i just wanted to make sure im doin the right thing.
    Thanks
    Will
    I dont just want to be another guy, with a pipe and a payment...


    1986 Honda TRX 250r
    1998 Yamaha YZ 125
    1990 Suzuki RM 250
    1986 Kawasaki JS 300
    1986 Kawasaki JS 550

  2. #2

    Default

    well u can take the head off and check the gap off the rings and the wall u can call a dealer or a bike shop and get that becuse if it feels like that the might be to samll of a gap and not geting enuff oil throw and scoring ur walls wich wud make it feel like its got grat compreshon becuse ur just comperesing old air and ading new at the same time becuse the pip foris some old air back in to the cylinders so id check the gap and im not trying to be a dick if im exsplaning some thing to u that u might allredy know but thats the only way i know to exsplane it
    if it ant mud it ant fun

  3. #3
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    Default

    I have checked the ring end gap and checked the cylinder wall clearence and its all perfect within spec. Im running plenty of oil at 32:1. I just want to know if its going to detonate with pump fuel? I think my squish is about 1MM. and all my ports line up perfect at BDC so i dont think anything can be wrong there.
    Last edited by Bad Ass Honda 250r; 04-29-2011 at 04:25 PM.
    I dont just want to be another guy, with a pipe and a payment...


    1986 Honda TRX 250r
    1998 Yamaha YZ 125
    1990 Suzuki RM 250
    1986 Kawasaki JS 300
    1986 Kawasaki JS 550

  4. #4
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    Default

    SO i need help right away, leaving at 5 tomorro morning for the race, I checked my compression and its 185. I should be able to run just straight 91 and be fine correct? I need an answer ASAP!
    Thanks
    I dont just want to be another guy, with a pipe and a payment...


    1986 Honda TRX 250r
    1998 Yamaha YZ 125
    1990 Suzuki RM 250
    1986 Kawasaki JS 300
    1986 Kawasaki JS 550

  5. #5
    Join Date
    Apr 2006
    Location
    Grand Rapids, MN
    Posts
    4,551

    Default

    yes, 91 will be fine, but i recommend finding a fuel that is non-oxyigenated...
    2006 Yamaha YZ250
    KYB SSS Suspension w/ Race Tech Gold Valve
    RB Designs Head
    ASV F3 levers
    Tag Metals Triple clamp
    Pro Taper Bars
    IMS Pro Series Pegs
    Motion Pro Twist Throttle Assembly
    VF3 Reeds
    Dunlop Geomax MX 51 Tires

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  6. #6
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    Default

    I re checked the compression after complete break in. (one race) haha, and it reads 200 even now. Im sorry for so many questions, but this should be a 50-50 mix of race fuel and 91 correct?
    Thanks
    I dont just want to be another guy, with a pipe and a payment...


    1986 Honda TRX 250r
    1998 Yamaha YZ 125
    1990 Suzuki RM 250
    1986 Kawasaki JS 300
    1986 Kawasaki JS 550

  7. #7
    Join Date
    Mar 2007
    Location
    Vacaville, California
    Posts
    6,464

    Default

    I would run 50/50 in it. I run 50/50 in my CR and it's stock compression.
    E2S MODERATOR


    1993 Yamaha Wave Runner VXR650

    2006 Yamaha PW50
    1975 Suzuki TS185

  8. #8
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    Apr 2006
    Location
    Grand Rapids, MN
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    Default

    250 PSI and on pump gas here with no detonation.
    2006 Yamaha YZ250
    KYB SSS Suspension w/ Race Tech Gold Valve
    RB Designs Head
    ASV F3 levers
    Tag Metals Triple clamp
    Pro Taper Bars
    IMS Pro Series Pegs
    Motion Pro Twist Throttle Assembly
    VF3 Reeds
    Dunlop Geomax MX 51 Tires

    Thanks to my sponsors:
    Duner Central
    X-Brand Googles

  9. #9
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    Default

    Quote Originally Posted by MX86 View Post
    250 PSI and on pump gas here with no detonation.
    Stock squish, squish band, porting, bore and cylinder? How are you doing this?
    I dont just want to be another guy, with a pipe and a payment...


    1986 Honda TRX 250r
    1998 Yamaha YZ 125
    1990 Suzuki RM 250
    1986 Kawasaki JS 300
    1986 Kawasaki JS 550