SBP Expansion on Skyhawk 48cc

Discussion in '2-Stroke Engines' started by geebt48cc, Jul 30, 2010.

  1. geebt48cc

    geebt48cc Member


    AWESOME, is the closest word I can fine. One question? After I installed everything improved, but why does it now run the best when choke is only half way off? :devilish:


  2. Pablo

    Pablo Motored Bikes Sponsor

    Interesting. What does your plug look like? Have you checked the carb tuning instructions in the install manual?

    Assuming you don't have an air leak (strong possibility) it sounds like you are running too lean, which seems a bit odd.
  3. geebt48cc

    geebt48cc Member

    Yes, the NGK looks just right........Tan like pic.

    Hey, ty.............
  4. AussieSteve

    AussieSteve Active Member

    Glen, I agree with Paul. Sounds suspiciously like an air leak.
  5. geebt48cc

    geebt48cc Member


    Steve, it runs great, but you've got to get the choke lever set just right before it will. Wonder what it could be considering the only part that was touched was obiously the exhaust for the new expansion pipe?:whistling:

  6. AussieSteve

    AussieSteve Active Member

    That's definitely a symptom of a lean mixture. If you didn't remove the carb while fitting the expansion chamber, possibly it got knocked or something and shifted to cause a leak.
    All I can suggest is that you double-check for leaks at both ends of the intake tube, then if it's still lean, you might need to raise the slide needle and/or go up in main jet size.
  7. geebt48cc

    geebt48cc Member

    The bike has very good free RPM's now, but the only thing I've noticed is that it really doesn't have anymore lower end torque? So, acording to the directions for a smaller 48cc you don't want to shorten the pipe any for that?........Just leave well enough alone?

    See, it will run up into the mid 30's now.............but I try to keep it around 20's. I'm just trying to figure out how I can tune it for a little better torque. (They say not to for smaller motors?) Uno, 1/4" either way.
  8. Pablo

    Pablo Motored Bikes Sponsor

    First move the needle up a notch or two - or have you solved that already?

    49cc engines really have little torque, no matter what - but you can tune it with the pipe a little.
  9. srdavo

    srdavo Active Member

    IMO--- The best improvement for more torque (in the speed range you like) would be to change to a 48 or 50 tooth rear sprocket.

    my 2ยข


    Check with member Skyliner70cc -- he had some of these sprockets for sale.
    Last edited by a moderator: Dec 18, 2015
  10. geebt48cc

    geebt48cc Member

    Low end on expansion pipe

    Hi room,

    I just got back from about 5k's. The expansion pipe on the 48cc Skyhawk is very nice . It does have much better top end, but it's slower to get there. Lower end to mids are not as good as stock muffler was. I've just put expansion pipe on. (zero tuning)

    Can I tune for better low's to mid's?.......Otherwise, FANTASTIC SBP's!

    Once again, TY

    Glen :D
  11. Ghost0

    Ghost0 Guest

    What is your header length? Measure the distance from the exhaust gasket to the start of the expansion chamber. Odd you mention more top end but less torque. Most others report almost the opposite, big gain in bottom end and modest gain in top end. Still sounds like a carb tuning problem to me.
  12. geebt48cc

    geebt48cc Member


    It's all original from SBP. I haven't touched...........(Yet) Runs great, idles great, but dosen't have as much lower end (torque), but more top end speed!.........Even smoother.....!~

    See, with stock muffler on this Skyhawk 48cc, it had more at lower end, but much better now at high end RPM's!~~?

    Go figure? TY,

  13. Ghost0

    Ghost0 Guest

    You could try adding a 1/2 to the header. Stock is 2.5 inches. Try 3 and see if that helps.
  14. Lazieboy

    Lazieboy Member

    Does the chamber make it quieter.
  15. AussieSteve

    AussieSteve Active Member

  16. Pablo

    Pablo Motored Bikes Sponsor

    Agree. No.

    Buttttttttttttttt if you put a muffler on the end of the silencer, it's a bit quieter and a heck of a lot less irritating than stock.
  17. Lazieboy

    Lazieboy Member


    Pablo, how about some more info on the silencer. can i make this. easy. I would'nt mind quieting down a bit. I hear a normal scooter go by and its quiet. It sounds like i'm riding a lawn mower threw the woods. Ha ha
  18. Pablo

    Pablo Motored Bikes Sponsor