Dyno run on KTM 620 RXC

Discussion in 'Thumpers' started by Beez, May 6, 2005.

  1. Beez

    Beez Given to fly

    Joined:
    Aug 20, 2004
    Oddometer:
    6,016
    Location:
    Framingham, MA
    Rebirth is complete! After riding the mighty LC4 only once last year and putting it away disgusted due to how awful it ran with the Quicksilver carb, it is now all the bike it can be! Don’t ask me how I put up with that carb all this time.

    Winter mods included selling off the Big Gun system (too loud!), reinstalling stock headpipe and a new SXC muffler (less sound = more ground), mainshaft bearing swap, valve adjust, starter clutch replacement and a Mikuni TM40-6 carb. I got the carb from Carburetor Parts Warehouse and they set it up with jetting similar to the Flanny guide and what most TM40 users have.

    So the big moment comes to start it and it is just idling super crappy, the mixture screw is doing nothing and the idle is hanging up. Blip the throttle and it just stays there. I changed the 17.5 pilot to a 20 but that didn’t help. So I decided that since I don’t have much jetting experience and an event I want to ride at the end of May I’d let the pros figure it out. Off to the dyno I go.

    To get the idle right we ended up drilling the pilot to about a 30 then we strapped it to the dyno and it made 40.4 hp and 35.0 ft.-lbs. torque but the air/fuel ratio was off the chart rich. That was with a 160 main, ended up with a 145 main and the needle in the second clip from the top. That netted 47.7 hp and 40.8 ft.-lbs. torque with the air/fuel ratio in the correct area.

    The bike is transformed. Smoother running and better power plus easier starting. What I paid the dyno shop I gained in less frustration, time to sus the bike before the 4 State and knowledge that the jetting is right. Only thing left to do is RIDE IT!

    I wonder why my final jetting specs differ so much from others with a TM40? Oh yeah, I have the dyno charts if anyone is interested but I don’t have a way to post them.
    #1
  2. accadacca

    accadacca Hard Rocker

    Joined:
    Jan 21, 2005
    Oddometer:
    156
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    South Jordan, UT
    Cool! Sounds like your summer will ne a blast! :ricky
    #2
  3. txrider

    txrider Been here awhile

    Joined:
    Mar 14, 2005
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    Cause a lot of folks jet em way too rich :)

    Congrats, I'll be taking my 620 and my 625 in some time this summer for the same treatment. Dyno with AF sensor rox.
    #3
  4. Rocamojo

    Rocamojo Toasted on both sides

    Joined:
    May 6, 2004
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    From Deep in the Dez
    Beez,

    So just for the record, you ended up with a 30 pilot??
    #4
  5. Esteban

    Esteban Banned

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    Above Golden
    I had the same experience.
    Everybody including Sudco recommended around a #170 mainjet for my fcr 41 here in Denver. HOG WASH !!!!
    The dyno proved that I needed a #135 main jet to get the proper air/fuel ration. My HP went from 43 to 50.
    #5
  6. Beez

    Beez Given to fly

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    Yeah a #30. Well, the tech drilled my #20 to a #30.
    #6
  7. pennswoodsed

    pennswoodsed lizards,bugs and me

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    Jan 20, 2007
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    Reading,Pa
    Did you ever use a factory #30 or do anything else with jetting ?
    #7
  8. Beez

    Beez Given to fly

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    Aug 20, 2004
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    No the only thing I did after the initial carb swap and dyno run was to change the choke knob to a different one. I also did the T-mod for the vent lines. I rode it for several years with that carb and pipe combo and sold it a few years ago.
    #8