Tuning your expansion chamber and Carburetor

Discussion in 'High Performance Bicycle Engine Tips and Motorized' started by Keef B, May 10, 2016.

  1. Keef B

    Keef B New Member

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    I'm trying to understand how to get the most performance out of these engines..

    Can anyone explain what it means when people say the following:


    KX-65 expansion chamber exhaust pipe that has been tuned for high RPMs,Keihin carb that has been re-jetted for this engine (& pipe), (this was a post I saw on craigslist for a bike)

    How do I know what jet size 65,70, etc etc to use in regards to what expansion pipe I have. Also does this have anything to do with how you port the cylinder jug meaning the size and shape in regards to the pipe on the exhaust side?? Also what about the intake side does that have anything to do in regards to how to you tune the carb and what pipe you choose.. Basically what's, when, where, why how's of this.


    I apologize if this question was posted before I apologize.

    Thanks fellas

    as always ride safe PEACE..
     
    #1 Keef B, May 10, 2016
    Last edited: May 10, 2016
  2. Greg58

    Greg58 Well-Known Member

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    There's a lot to tuning to a expansion chamber, the shorter the head pipe is from the flange till it flares into the chamber the higher the rpm range is before you hit the power band or it starts producing felt power. Different lengths from flange to the cone at the stinger will change the power band.
     
  3. Greg58

    Greg58 Well-Known Member

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    #3 Greg58, May 10, 2016
    Last edited: May 10, 2016
  4. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    The CL ad you are talking about is mine... http://losangeles.craigslist.org/wst/bid/5568219674.html

    As Greg said above, there is indeed a lot of hours that go into properly tuning a pipe & carb to work with any engine.
    You have to test (& re-test) different header/ stinger lengths & carb jets until you get the best performance; (& believe it or not), the size of the sprocket also plays a big role in tuning the pipe.
     
  5. Greg58

    Greg58 Well-Known Member

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    Good looking bike Norm.
     
  6. KCvale

    KCvale Active Member

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    'Tuning" and expansion chamber exhaust is all about wave timing.

    This is how they work.
    Follow the green mixed gas.

    [​IMG]

    All I can offer beyond that is I never have to jet a carb in Phoenix, and with a SickBikeParts expansion chamber it's single straight copper pipe length is perfect for a 48cc engine. Cut it in half and its perfect of a 66cc.
     
  7. Keef B

    Keef B New Member

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    Fellas,

    Thanks for clarifying things for me guys this info really helps Greg58 I will check out that link read up on this more.. But it makes sense shorter header means higher RPM's. Yes "Venice Motorbikes" that is exactly where I got it from was your CL post. I freaking love that bike I check it out everyday (Wish list bike)lol lol . What I have now is a 32 Tooth sprocket, Jakes diamond head, port cylinder jug with a long stretch expansion chamber pipe. Which I assume I would need to tune for Higher RPM's since that sprocket is small. I'm looking at getting the reed valve setup & cylinder from gas bikes.com. Right now im debating on getting a Yamaha kx85 or Honda cr 80 pipe have it modified to fit or buying the Big bertha pipe from MZMIAMI on e-bay.
     
  8. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    Something to keep in mind... Those factory motorcycle pipes are way better than any other pipe out there, but you'll have to cut & weld it to fit your bike (& you'll also have to make a header that bolts it onto your engine).

    I can do it all if you need it done.
     
  9. Keef B

    Keef B New Member

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    I was thinking the same thing?? Do you have access to get those pipes?? Send me a PM with you prices on muffler modifications.
     
  10. JOBAfunky

    JOBAfunky New Member

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    OK, so I just got my banana expansion chamber on my beach cruiser last night. It was tough though. I got it to where the pedal just barely scrapes it and into the 1cm window of clearance between the front tire and the crank bearings. So I don't think I'll have room for any kind of extension pipe. It's a 66cc engine with a low compression huge Puch head on it. I'm noticing an occasional loud pop when idling, and I get it to quiet down when I gently throttle. I didn't get the low end power boost I was looking for. Maybe a little in the low middle. I have a racing carb with a bunch of jets, any advice on which way I should adjust?
     
  11. BobbyT

    BobbyT Member

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    JOBAfunky,
    My advice on tuning your new banana pipe is walk to a cliff and throw it like a boomerang. If it dosn't come back buy a real expantion chamber and start tuning with that. If you have problems with your new racing carb go back to your NT. You can get good results with stock parts.
     
  12. BobbyT

    BobbyT Member

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    JOBAfunky,
    My advice on tuning your new banana pipe is walk to a cliff and throw it like a boomerang. If it dosn't come back buy a real expantion chamber and start tuning with that. If you have problems with your new racing carb go back to your NT. You can get good results with stock parts.
     
  13. JOBAfunky

    JOBAfunky New Member

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    Nice, There's no way I'm dropping serious money on on a part that has a high chance of not fitting. My carb if fine I was just seeing if anybody knew if I should lean or richen the mixture.
     
  14. Chaz

    Chaz Active Member

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    The best way is to check the colour of your spark plug. The general rule is that you may have to jet richer. The expansion chamber is likely less restrictive than the stock muffler. When you replace the stock muffler with an xchamber you are creating a leaner condition in most cases.

    Not every banana is the same. One is an expansion chamber with no baffles and one has baffles to act a bit like a muffler.

    Also, in simple terms, the shorter the header pipe the higher the rpm power band. And, of course, the longer the header pipe the lower the rpm power band.
     
    #14 Chaz, Oct 26, 2016
    Last edited: Oct 26, 2016
  15. Bass ackwards

    Bass ackwards New Member

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    If you need performance always start from the inside work your way out these Motors are out of balance on purpose because they're running bass ackwards during compression stroke the Piston is pushing for words toward the exhaust port if you increase performance you will burn your piston balance the crank Spin jug and piston around which takes very little porting mix your fuel ratio 50 to 1 now your engine will run way cooler and is ready for your outside mods
     
    #15 Bass ackwards, Dec 21, 2016
    Last edited: Dec 21, 2016

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