Removing welch plug HuaSheng 49cc 4 stroke

Discussion in 'High Performance Bicycle Engine Tips and Motorized' started by Mike_Honcho, Jan 10, 2019.

  1. Mike_Honcho

    Mike_Honcho New Member

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    I though i would just post these pics to help, although i still don't know why I would make the bike run a little richer... The motor is running fine before removal, higher rev?
     

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  2. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    That's a idle circut screw.... Without it you will have a lot of trouble making the engine idle & run properly.
     
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  3. Tom from Rubicon

    Tom from Rubicon Active Member

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    That "was" an idle circuit screw. It did have a driver slot to adjust it. The counterbore just to the right is the plug you wanted.
    Norm correct me if I am wrong.
    Carbs a cheap. Welcome to the club.
    Tom from Rubicon
     
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  4. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    You're correct.... that was a idle screw!

    Actually, this would be a great time to swap out that carb for a 2-stroke carb conversion! ;)
     
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  5. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    He removed the correct plug.
    The plug covered the air mixture screw.
    Do not remove the plug in the counterbore just to the right.

    [​IMG]
     
  6. Tom from Rubicon

    Tom from Rubicon Active Member

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    Norm, I have a first build HuffyDavidson with carb trouble. What 2stroke carb do you recommend?
    Tom from Rubicon
     
  7. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    Tom, this is it... https://www.gasbike.net/collections/4-stroke-parts/products/4-stroke-nt-carburetor

    This is a much better manifold... https://www.gasbike.net/collections...s/49cc-nt-carburetor-intake-for-4-stroke-long

    If you use this carb?, you'll probably have to install a slightly larger jet. (or just drill it if you can get a 'jewlers' drill bit set)
     
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  8. Tom from Rubicon

    Tom from Rubicon Active Member

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    Thanks for the info Norm. what diameter drill. I'm a Tool and Die Maker with many drill sets.
    Tom from Rubicon
     
  9. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    Stock NT jet is a 70 so try a #69 drill bit
    Use number drills.

    #BitSize Inches Millimeters Jet Size

    #80 0.0135 0.3429 34.29
    #79 0.0145 0.3683 36.83
    1/64" 0.0156 0.3969 39.69

    #78 0.016 0.4064 40.64
    #77 0.018 0.4572 45.72
    0.5mm 0.0197 0.5 50

    #76 0.02 0.508 50.8
    #75 0.021 0.5334 53.34
    #74 0.022 0.5715 57.15

    #73 0.024 0.6096 60.96
    #72 0.025 0.635 63.5
    #71 0.026 0.6604 66.04

    #70 0.028 0.7112 71.12
    #69 0.0292 0.74168 74.168
    0.75mm 0.0295 0.75 75

    #68 0.031 0.7874 78.74
    1/32" 0.031 0.7938 79.38
    #67 0.032 0.8128 81.28

    #66 0.033 0.8382 83.82
    0.85mm 0.0335 0.85 85
    #65 0.035 0.889 88.9

    #64 0.036 0.9144 91.44
    #63 0.037 0.9398 93.98
    0.95mm 0.0374 0.95 95

    #62 0.038 0.9652 96.52
    #61 0.039 0.9906 99.06
    1mm 0.0394 1.0 100
    #60 0.04 1.016 101.6
     
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  10. Tom from Rubicon

    Tom from Rubicon Active Member

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    Thanks for the come back MBR #69 it is.
    Tom from Rubicon
     
  11. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    I usually drill two sizes bigger, but your engine might want something different.

    If you feel you've drilled too big?, you can easily close the jet hole with a pinhead size dot of electrical solder & re-drill it to a smaller size. ;)
     
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  12. Tom from Rubicon

    Tom from Rubicon Active Member

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    Hey Norm,
    #68 drill is logical, .003 larger won't over feed the engine.
    Run it and give the sparkplug a hard look.
    Been screwing around mounting Wald fenders on my Sportsman 80. Thanks for the input. Hope Mike is absorbing all this good info.
    Tom from Rubicon
     

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