Tuning QMB139

[ton3s]

Hi all, after advice....

Looking for improvements on 50cc, has aftermarket exhaust and upgraded jets (#79 main and #33 idle), stock size 18mm carb with pod filter (main jet couldn't handle the airbox restrictions, and would die at higher rpms).

Performance increase (if any) barely noticeable, wondering if I remove the baffle at the end of the exhaust to flow more freely might make a difference?

Idle mix been dialled in for best engine rpms, does bog a tiny bit initially from idle when blip the throttle, but if I lean the idle mix anymore rpms drop. Plug colour looks good after road test.

Performance variator fitted for smoother acceleration, 4g weights because anything over 4.5 just wouldn't let it rev and made it slooooow.

- keen for any expert recommendations

 

[Heinz]

Jet 79 with a pod filter shouldnt work. Lose the pod filter. Use heavier weights around 6g.

 

[ton3s]

Jet 79 with a pod filter shouldnt work. Lose the pod filter. Use heavier weights around 6g.

Couldn't run without the pod, too rich just died (even set the needle low as I could) experimented with weights, 5g (or heavier) we're painfully slow. Factory variator I believe had 6g weights, variator I'm running has more ramp travel and more linear acceleration (top speed no change)

 

[C-Row]

what max speed are you getting? over here the consensus is "slap 80 cc on" and be happy with 75 km/h top speed.
i doubt a "performance exhaust" with or without baffle would help: have you seen the tiny valves and ports in the head of one of these engines?
what valve lash have you set to?

 

[ton3s]

what max speed are you getting? over here the consensus is "slap 80 cc on" and be happy with 75 km/h top speed.
i doubt a "performance exhaust" with or without baffle would help: have you seen the tiny valves and ports in the head of one of these engines?
what valve lash have you set to?

65kph with a tail wind no, haven't checked/adjusted valves, although probably should check that! We have another Chinese scoot in the family that will comfortably do 75, no idea why

 

[Heinz]

Couldn't run without the pod, too rich just died (even set the needle low as I could) experimented with weights, 5g (or heavier) we're painfully slow. Factory variator I believe had 6g weights, variator I'm running has more ramp travel and more linear acceleration (top speed no change)

Very weird, I cant believe the scooter is set up right in this way. No wonder it will stay slow. There must be something wrong with it.

 

[ton3s]

Very weird, I cant believe the scooter is set up right in this way. No wonder it will stay slow. There must be something wrong with it.

Could be the Amazon $30 carb? Was fine on the stock one, might change it back. Variator was a worthwhile upgrade, once I got the weights it needed to rev properly.