1. Husqvarna Motorcycles Made In Sweden - About 1988 and older

Mikuni Carb Intake Difference?

Discussion in 'Vintage/Left Kickers' started by vintagecs, Oct 17, 2014.

  1. vintagecs Husqvarna
    AA Class

    Location:
    Lebanon, IN
    Husqvarna Motorcycle:
    '78 390OR, '76 360 Auto, '74 125SC
    Other Motorcycles:
    Penton, Yamaha
    I need to rebuild some carbs for a 78 and 79 390 Husky and I have several carbs with the large intake bell. They are too long to fit well in the bikes, and I was wondering if I cut the bell down would it affect performance? The carbs look identical in every other way. Also, what models did the larger intake fit? All of my other 78-80 bikes are smaller, like the one on the right.

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    vintagecs, Oct 17, 2014
    #1

  2. ruwfo Administrator

    Location:
    NJ
    Husqvarna Motorcycle:
    1980 390CR, 1982 430CR, 1984 400WR
    Other Motorcycles:
    1985 250XC, 2016 FJ-09
    Yes the space between the carb & the air box/air filter makes a difference. On a 2 stroke RD400 I had, it had the 4 grand
    carb flat spot, they all have stock. Put a spacer in between the back of the carb & filter & the flat spot magically when away.

    I guesses like the swirl affect inside the cylinder, there's one from the air filter too. If the cylinder is pulling in fuel from the carb, it's also pull in air thru the filter, so the spacing make a difference.

    Husky John
    ruwfo, Oct 17, 2014
    #2

  3. grouty Auto Lover ...

    Location:
    South West UK
    Husqvarna Motorcycle:
    78 390WR, 78 390 AMX, 500 Humph
    Other Motorcycles:
    works 73 CCM 520, another 73 CCM520
    The original 38mm Mikuni carbs I have here have the shorter inlet. The new one I bought a few years ago has the longer one.
    It is possible that the aftermarket (non-Husky specific) are
    generically longer.
    grouty, Oct 17, 2014
    #3

  4. Bill502 Husqvarna
    AA Class

    Location:
    Upstate NY
    Husqvarna Motorcycle:
    2007 WR167 1978 CR250 1938 sw maus
    Other Motorcycles:
    1970 Triumph T100C 1973 Honda TL125
    If all dimensions are the same I would have no problem cutting the intake.
    Bill502, Oct 17, 2014
    #4

  5. suprize Husqvarna
    Pro Class

    Location:
    Bendigo, Australia
    Husqvarna Motorcycle:
    WR 400, bike in a box Moto Villa 350
    Other Motorcycles:
    ktm 300
    mate had the same prob with his PE, new mikuni was substantially longer in the bell. he got it turned down in a lathe, works fine.
    suprize, Oct 17, 2014
    #5

  6. motomwo Husqvarna
    AA Class

    Location:
    Imbler Oregon
    Husqvarna Motorcycle:
    Many vintage big bore and automatics
    Absolutely, you can cut down the airbell to the same length as the short style. And yes the lathe works best and the easiest way to do it. I have personally done this many times. It won't effect performance as the rubber air box boot acts as part of the air intake track. I beleive the longer style carbs started being used on the 1983 models. Hope this helps!

    Marty
    motomwo, Oct 17, 2014
    #6