20mm Walbro on a China Girl

Discussion in 'High Performance Bicycle Engine Tips and Motorized' started by FFV8, Sep 19, 2014.

  1. FFV8

    FFV8 New Member

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    Tired of smelling like gas, and chasing jets, I wanted tuning & a fuel pump...

    [​IMG]

    Then some threads

    [​IMG]

    And install a hose barb

    [​IMG]


    .
     
  2. FFV8

    FFV8 New Member

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    The intake mounts at the same angle as the cylinder port - you can look straight through the carb in to the cylinder

    [​IMG]

    Add the crankcase pulse line

    [​IMG]

    I laser cut the carb flange to include the bracket for the cable,and cold formed it to locate the cable & return spring

    [​IMG]

    Even the stock intake nuts still fit.
     
  3. skitchfish

    skitchfish New Member

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    FF, That is nice work and excellent pics! I hope you do a follow up on your linkage and throttle. I feel that this is the downfall of the Walbro carb, unless your racing, the feel of a less than 1/4 turn throttle doesn't get it with me.

    The tuning aspect is unbelievable from bottom to top and in my own opinion is the best that can be had with such ease. I even used a old piece of excercise equipment to run my back tire under load in the garage. No four stroking anywhere, no screwing around!

    I will be very interested to see what you come up with for your throttle as i can not seem to eliminate it's total crap feel. Thanks, Skitch
     
  4. FFV8

    FFV8 New Member

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    The biggest problem with the throttle cable is a lack of a proper return spring.

    Trying to use the OEM spring on the butterfly will only lead to frustration. Without enough spring pressure the cable drags in the housing & feels mushy.

    I use a return spring with an adjustable preload, and fabricate the cable attach parts for the butterfly arm - smooth, consistent throttle operation is the result.

    .
     
  5. graydog8josh

    graydog8josh New Member

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    where is the rest of your cylinder?
     
  6. FFV8

    FFV8 New Member

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    It's laying right here. I just took it apart to port it, makes it easier to reach the transfers.
     
  7. SpecializedMountainMoto

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  8. FFV8

    FFV8 New Member

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    I don't think the saw kerf will leak much more than all of the damage from the broken rings & the missing chrome where the piston stuck. Should run as good as it ever did.

    .
     
  9. Davezilla

    Davezilla New Member

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    it'll still work... just use a little ultra copper and you're good... lol
    Anyway... Nice job on the intake you made
     
  10. curtisfox

    curtisfox Active Member

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    This has to be the best idea i seen in a long time, with all the carb trouble people are having. Jet changing, moving C clips, trying two or three different carbs ( none fast then the other ). Don't have a china engine myself,but have others. And have used chain saws for years and never had trouble tuning like the guys do with china tuning, and they can be run on 4 stroke as well. Just turn the high and low jets a little for fine tuning. The big thing about 2 stroke is measuring the gas right and the same every time you fill ...........Curt
     
  11. sbest

    sbest New Member

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    Cutting an old cylinder in half is an excellent learning tool.
    This was a Yamaha Blaster cylinder cut apart as a learning tool:
    [​IMG]

    From what I learned from it I stuffed it with several tubes of JBWeld epoxy in this manner (photoshopped):
    [​IMG]

    Which in real life looked like this comparison:
    [​IMG]

    The result was easier carb jet tuning because of fuel staying in suspension, wider powerband and of course, more power.
    All gleaned from studying a sectioned cylinder.

    Steve
     
  12. chrisme

    chrisme New Member

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    Where did you find that carb / what model is it? I've been having a hard time finding a non-return style carb with an external pulse line. You've found just what I'm looking for.
     
  13. cannonball2

    cannonball2 Active Member

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    You can also use the carbs with the internal pulse passage just by Dremeling a small channel/port into the manifolds carb mounting flange to allow the pulse in the intake to reach the port on the carb.
     
  14. chrisme

    chrisme New Member

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    Sure, however It would be nice not to have to deal with a fuel return. The external pulse port is just the icing on the cake with this carb!
     
  15. curtisfox

    curtisfox Active Member

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    Can one just take the return line and hook it the main fuel line from the tank, instead of going all the way to the tank?.............Curt
     
  16. FFV8

    FFV8 New Member

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    Porting the pulse circuit in to the intake is not the best plan.

    The fuel pump was designed to work with the crankcase pressure pulse as well as the intake vacuum. That drives the diaphragm both directions.

    With vacuum only, you get a half stroke of the fuel pump. This can make the high speed tuning very sensitive as the fuel pressure drops at WOT.

    I have carbs and manifolds on the shelf. Just finished making a new batch of throttle arms too.
     
  17. mike carter 2

    mike carter 2 Member

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    cool kit . are you still makeing them?
     

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