carb as a muffler?

Discussion in 'Motorized Bicycle General Discussion' started by the new ausped, Mar 6, 2010.

  1. the new ausped

    the new ausped New Member

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    so. i was thinking today (oh noes) about how to quiet down my mb and me grass cutter.

    what i was wondering was could you bung an old carby on the end of your muffler?

    basically.. pin the throttle open and you could use the choke as an adjustable baffle

    next Q. i do not have the parts or a welder or the money to get the parts, so could someone who has an old useless carb +a welder to stitch one on and see how it goes?

    bardico or someone was looking for an adjustable baffle and this may (just) work......
    thankyou and remember if this starts a phenomonomonomn (< thats how you spell it right?)
    my name and this sign ogoes on top auflg LOL
     
  2. K.i.p

    K.i.p New Member

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    ball valves, I'm just sayin
     

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  3. the new ausped

    the new ausped New Member

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    but thay cost $ im not asking people to spend money for somthing that may not wrok
     
  4. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    Model airplane engines used to use a "muffler throttle".
    You won't cut down the sound as much as you'll cut off your power.
    A muffler requires volume among other things.
     
  5. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    That sounded weird....what I meant was an effective muffler requires a voulumous area to redirect or dampen sound.

    You can even change the tone of your exhaust based on materials and material thickness of your muffler.
     
  6. K.i.p

    K.i.p New Member

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    It's nothing I am interested in experimenting with personally, but for anybody that is I figured cut to the chase and save some aggravation. Instead of replicating a valve with an entire carb, just use an actual valve. $3 maybe?
     
  7. stuartracing

    stuartracing New Member

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    The thing is , is the carb. is aluminum and the exh. pipe is steel.....Kinda hard to get them both stuck together and then to run a cable up to the throttle somehow.....At idle with the carb/muffler closed I would thing it would just stall out because of no flow out the carb./muffler....
     
  8. diceman2004

    diceman2004 New Member

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    i can,t speak to much for 2 strokes , but putting a valve in the exaust system will make your back preasure a variable , making it next to impossible to achieve an ideal jetting setting .

    you want your exaust system to flow at a constant .

    i think you are better off just experimenting with different size pipes and muffler tips and baffles .

    BarelyAwake has a good thread on a remote airbox , which he noticed quieted the engine down some .
    http://motorbicycling.com/f4/remote-airbox-intake-silencing-cheap-10967.html
     
  9. K.i.p

    K.i.p New Member

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    Hi diceman, I have to agree, it makes me wonder if a guy with some free time could dial in a sweet spot regarding back pressure in this manner? It's just a hypothetical question.
     
  10. diceman2004

    diceman2004 New Member

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    Well i,m not the guy to ask , i don,t know to much about 2 strokes .

    i do know that there is a formula to calculate how to build a properly sized expantion chamber ( i do not know the formula ) i,m sure someone on here does .

    all i know is that 4 strokes use back pressure more as a means of regulating flow .

    2 strokes rely more on the harmonics of exaust gas to help suck exaust from the cylinder , which is why theres such things as tuned pipes .

    iv,e read a lot of good comments on poeple using poo poo pipes .
     
    #10 diceman2004, Mar 7, 2010
    Last edited: Mar 7, 2010
  11. professor

    professor New Member

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    The sweet spot for back pressure is zero.
    I do not know where the myth came from in thinking you need some. Look at any race machine, unless the track requires them for noise control, you will see no muffler of any kind.
    To the OP- restriction in the exhaust WILL make the engine run quieter, along with no power, overheating and burned exhaust valves.
    A muffler or 2, and long pipes will quiet engines very well. Those cigar shaped Briggs muffs work pretty good too- real cheap.
     
  12. diceman2004

    diceman2004 New Member

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    i have 2 friends that used to drag race motorcycles ( i wont give up their secret ) but they would argue quite convincingly against having zero back pressure , even an oversized unrestricted header tube adds back pressure , and every bend in the tube also adds back pressure . Burnt valves come from running lean ( fuel-air ratios )

    generally speaking , a short pipe will give you more bottom end and a long pipe will give you more top end power

    every setup needs proper jetting for optimal performance .

    i totally tore down and rebuilt my yamaha roadstar engine myself to repair a faulty stator shaft . i run a wide open k&n intake , ported my own rubber intake manifold , and run a 3 inch exhaust . i do my own jetting . I USED MY BUDDIES SECRET and i added more power , and increased my mileage by 75 km per tank
     

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  13. K.i.p

    K.i.p New Member

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    I got my briggs/stock combo painted this weekend, it's super quiet and seems to work pretty well with the engine although I did replace the small exhaust tube on the stock end cap.
     

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  14. BarelyAWake

    BarelyAWake New Member

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    The only thing I've heard of even remotely like this is an exhaust cutout... which if installed after an expansion chamber on a two stroke - but before the muffler on either a 2 or a four stroke - allowing you to open a bypass to achieve full flow (and noise) or close it for that "stealthy" approach.

    If I thought there'd be enough of a gain on these lil bikes - I'd do it meself :D

    [​IMG]

    Having something after the muffler that simply closes I can't see doing any good for anything other than a back-up kill switch o_O
     
    #14 BarelyAWake, Mar 8, 2010
    Last edited: Mar 8, 2010

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