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  1. #1
    Tyetye
    Guest

    Default Bandit turbo hsr 42 set up

    Hello all.
    I'm looking for some help. I've never used a mikuni hsr42 so having a far problems with the set up.
    Here goes.....
    Suzuki bandit 600 running custom headers, garrett gt1749 vvt turbo on a DRAW THOU set up. K&N type air filter straight through exhaust.
    4 degree ign advance
    I'm running 25 pilot jet and 155 main. Neddle is on 2 slot from the top.

    The problem I have.....
    Start up hot or cold is fine, cold with choke.
    Idles sweet and will rev up and boost up fine IF I DO IT SLOWLY.
    If I RIP the throttle open the engine Boggs down.
    Should properly say I'm in the UK so the weather is around 18C

    Like I said I have never used a hsr42 so was hoping someone can point me in the right direction.
    Thanks

  2. #2

    Join Date
    Dec 2018
    Posts
    936

    Default

    Why in the world would you create a combination that you do not know how to tune? That is a serious question.

    There is a Mikuni tuning guide published by Sudco. I suggest you get a copy and study it.

    Jim

  3. #3

    Default

    Why not try something new / different , if you want to do that. It’s fun learning and a good sense of achievement when you sort it / get there and a good experience even if you don’t get there.
    Much better than just sticking to a known path .
    Perhaps the essence of customising ?
    But then again that’s my opinion !

  4. #4

    Join Date
    Dec 2018
    Posts
    936

    Default

    Quote Originally Posted by dowood1 View Post
    Why not try something new / different , if you want to do that. It’s fun learning and a good sense of achievement when you sort it / get there and a good experience even if you don’t get there.
    Much better than just sticking to a known path .
    Perhaps the essence of customising ?
    But then again that’s my opinion !
    That is why I recommended the Mikuni tuning manual. When you embark upon a new path, you are pretty much going to have to teach yourself. I could tell him how to tune that carb on a naturally aspirated motor, but add the turbo, and that is a MUCH more complicated problem. Any advice I were to give would probably do more harm than help.

    I will say this: on any slide carb, the NEEDLE is the thing. All other adjustments are peripheral.

    Jim

  5. #5
    Senior Member

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    Join Date
    Apr 2013
    Posts
    8,248

    Default

    An HSR 42 is excessive carb for a 600cc engine (which lest we forget has only one 150cc cylinder on the intake stroke at a time) and did exactly what too much carb does, bog and cause lag when the throttle is whacked open. When you whack the throttle open (which is not the ideal way to launch a turbocharged motorcycle) the turbo has no time to spool up AND you just suddenly dropped the VELOCITY of the air going through the wide open carb. Large bore carbs can't react quickly because they rely on pressure differential (AKA suction) to push fuel from the float bowl into the airstream. (The lay person concept of suction drawing fluid is a "mental convenience". Were there no atmospheric pressure behind it fuel would not flow from bowl to bore.)

    Randomly throwing that carb on as an experiment was fine. Now you know and can build on what you learned. Try a smaller diameter carburetor and modify your launch technique to better use the turbo. A bit of study first would have helped. All induction mods are reinventing the wheel at this point so find builders who did what you want to do.

    Study theory of operation. Read up on draw through systems. Post results! It's an interesting project.
    Last edited by farmall; 4 Weeks Ago at 4:24 AM.

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