sbp expansion chamber?

Discussion in 'Motorized Bicycle General Discussion' started by bluenosegoat, Jan 22, 2010.

  1. bluenosegoat

    bluenosegoat New Member

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    I just ordered my Hd shift kit today so obviously I need a new "want to have" item. I have what i believe is a 49cc engine. I still havent measured the stroke but the bore is 40mm. I am very curious as to how loud these expansion chamber pipes are. I like mine fairly quiet and I'm surprised how quiet it is with the stock muffler. Will the expansion chamber still produce good results with out any other mods like carb, porting cylinder, or compression increases? Would it be a waste of money with out some or all of these other mods?
     
  2. Mac

    Mac New Member

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    Bluenose,
    I have a PK80 slant. There was a world of difference in power with a pipe. A big difference without "Tuning" (adjusting the length) right out of the box. As far as noise, the SBP pipe is pretty quiet during normal operation, if ya crank on it and it "comes on the pipe" I don't think it's much louder than stock, noise is coming from behind you(in my case).
    Hope that helped.
    Mac
     
  3. bluenosegoat

    bluenosegoat New Member

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    Thats what i wanted to hear or not hear! Thanks, I'm just gonna have to get one. I dont mind the noise, but the less noise I make the less attention I grab. So is the sbp pipe the only one that is tunable out of the box with out modification/welding? Are they real heavy?
     
  4. Mac

    Mac New Member

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    All you have to do to tune it is first have the motor running well BEFORE you put the pipe on, install pipe, warm it up with a short run, do a full throttle run for approx. 1/4 mile, hit kill switch @ full throttle, let cool, read plug.(this checks the Carb. rich/lean) adjust "C" clip as needed, repeat as needed, (sounds simple and quick, not always) if your close with the carb, you will feel a big difference, since your running a 49cc, they usually rev a bit higher, you may want to shorten, instructions come with the pipe or are on SBP web site.
    The weight is just right, not to heavy but durable, I welded a bracket on mine with a MIG welder, no burn thru issues, just don't fall asleep while your welding on it or get a shop to do it.
    Hope that helps
    Mac
     
  5. bluenosegoat

    bluenosegoat New Member

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    Great! I was little concerned about the weight remebering the pipes from yz dirt bike being fairly hefty. Good to know they are thick enought to weld some mounting brackets. Definatly on my list for next upgrade.
     
  6. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    Fully assembled the pipe weighs just over 3 pounds.

    If you want really quiet, slap the muffler on after the silencer.
     
  7. bluenosegoat

    bluenosegoat New Member

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    Thanks Pablo, I think I will be putting it on my sons bike as he is having trouble keeping up with me now and soon (hopefully this coming weekend) I'll have that shift kit on!
     

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