2003 yz250f with Lectron - help.

Discussion in 'Bike Mods, Performance, Maintenance & Repair' started by rockclimber, Oct 19, 2008.



  1. rockclimber

    rockclimber Rookie DRN Member

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    Please help. I ride Michigan single track woods trails for recreation.

    BIKE: I just purchased a used 2003 Yamaha yz250f with a Lectron carb installed, and a Yoshimura TRS exhaust. The Lectron carburetor has only a few markings; patent 4008298, a number "44" stamped onto the thin vertical upper portion, and a "Pure Boost" sticker fixed to the thin vertical upper portion. Can't find a specific Lectron model number anywhere.

    :bang: PROBLEM: The bike's idle is very high, and has great accerleration from that high idle. This might be desirable for racing, but I'm trail riding and with the high idle there is no engine-brake into the corners. When I reduce the idle to 1900 rpm, then the bike stalls upon attempted acceleration from a stop. Also, the bike starts very hard after each stall - 20 kicks, but starts 10 kicks cold. New spark plug is black, but not sooty.

    NOTE: Lectron customer service is absolutely useless!!! They wouldn't give me the time of day.


    HELP: Please advise. What are the default carb settings? And how should I re-tune this carburetor for normal idle and smooth roll-on power? Current C=52.5 mm and idle screw is 2 turns out.
  2. _JOE_

    _JOE_ Subscriber

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    Sounds like the pilot circuit is rich. Where do you have the fuel screw?
  3. _JOE_

    _JOE_ Subscriber

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    Is there an accelerator pump?
  4. rockclimber

    rockclimber Rookie DRN Member

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    No accelerater pump.

    There are three adjustable screws. One is the idle screw, which I believe simply turns against the slide to adjust the idle rpm. The second is between the slide and the air box end of the carb air intake; and this screw is closed due to it is apparenly used only for racing to prevent stall during long jumps. And the third is what I believed to be the 'air' adjustment which is slightly below and forward of the idle (rpm) adjustment screw.
  5. Rich Rohrich

    Rich Rohrich BioHazard

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    You'll never, ever get the Lectron to work well in a transitional throttle environment like woods riding. Find the proper Keihn FCR and change it out. Used FCRs are available all the time.

    The Lectron works great in simple straight to WOT applications like drag racing, and CVT based engines. It has no place on a woods or an MX bike.
  6. rockclimber

    rockclimber Rookie DRN Member

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    Thank you. I suspected I may need an original carburetor. Please post a few websites that I might find a used Keihn FCR carburetor for my 2003 yz250f?
  7. Rich Rohrich

    Rich Rohrich BioHazard

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    Ebay is the obvious place to look first. There are a lot of these bikes that get parted out so used carbs are fairly plentiful.
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