Instructions for de-restricting Super 8 50cc

[wheelsoffreedom76]

   Top speed unchanged, or at least not noticeable. Disassembled both clutches down to driven pulleys and measured belt depth in each and discovered the seemingly unrestricted pulley does not allow the belt to travel any deeper than the kymco pulley. Well, it does a few 64th's of an inch if that counts. See my picture for visual of maximum belt depth that each pulley will allow.

   The generic qmb clutch has multiple build flaws, and would only be reliable as a paperweight.

The picture below shows how the generic qmb139 clutch driven pulley does not allow any further belt depth than the original Kymco part. 

[scootergrisen]

Are the torque drive all the way out on the picture ?

On my scooter it looks like it goes out more.

[wheelsoffreedom76]

Are the torque drive all the way out on the picture ?

On my scooter it looks like it goes out more.

  Yes, both torque drivers are all the way out in the pic. Will a belt fit further into the pulleys you have?

[scootergrisen]

I don't know i'm not sure. I just assumed it would go all the way down.

[wheelsoffreedom76]

     Results of marking the pulleys and running it.

   It appears the clutch pulley reaches it's maximum belt depth, and the variator reaches right at maximum travel about evenly.

  On stock exhaust, stock variator and clutch pulleys,  no rev limiter (it seems the stock exhaust is the rev limiter), upjet, it seems around 37 mph indicated is about it. Going any faster would take mods to facilitate higher engine rpm (pipe, bbk, carb, airbox). Or final drive gearing changes.

  If it had a clutch pulley that allowed the belt to travel to the bottom, the stock variator travel would only facilitate using around 70% of the clutch pulley range, the belt would have to be shortened to allow the stock variator to pull it to the bottom of the clutch pulley, and thus some penalty to the takeoff gearing.

  A larger variator with more effective travel would be ideal with a fully unrestricted clutch pulley.


  Just my interpretation of it, let me know what you think, and what results you have found.

[wheelsoffreedom76]

pic #2

[wheelsoffreedom76]

   I removed the restriction from the stock exhaust. Acceleration is much improved, and top speed is somewhere past 40 mph, I backed off at 40 but it was still pulling. Prior to this mod, 35-37 mph was it and had to hold wide open for a little bit to get there, now it pulls right past those speeds quickly.  The throttle response is much more banshee like than before.   The tube extends into the exhaust pipe about 3/8", so you have to grind out the weld to get the tube out of the pipe. I cut a round piece of sheet metal, and made a gasket out of some header material and triple clamped it, since I couldn't get it welded today.  I cut the air injection tube off and crimped it shut.

[wheelsoffreedom76]

 The sealed off hole. I was gonna have the weld shop tig a cover on it, but they were busy today.

[wheelsoffreedom76]

  Crimped off air inlet tube.

[pmoneysuper850]

so the restriction is in the pipe itself not in the airbox?

[Nori]

on 2t yup but not sure for 4t
there is also a topic for modding stock pipe and getting 10+km for top speed

[wordslinger]

..wonder if the cobra has that...