I always thought the Spree would be a good starting point for a low-performance 50cc offroad bike. The job you're doing with the Express looks much like I'd envisioned.
You have a couple of options for speed limiting.
1) Restrict throttle opening with slide. Put washers or machine in a screw to limit upward travel on the slide.
2) Restrict throttle opening with restrictor plate. Put a plate with a hole between carb and thermal plate (brown piece.) Done all the time to restrict race cars and bikes.
3) Restrict exhaust. Weld washer into the exhaust
4) Re-gear. Change pulley ratio up front and run a different size belt.
Any of above would work. I'd try #4 first and then do the others.
Re: thumb throttle. Good idea in concept, but at some point she'll need to learn how to use a grip throttle. This is all about initial hand positioning and should be taught early. I had a death grip experience once at 10, didn't learn correct positioning until 20 years later in MSF.
On changing the pulley ratio. On the front drive faces, machine material off the outside of the drive faces, then put spacers (washers) between the drive faces to move them apart there by reducing the drive pulley diameter so the belt runs lower in the pulley assembly. Instant lower ratio.
Bear 45/70
'83 Aero 80 X 3
'84 Aero 80 X 3 '85 Aero 80 '84 Aero 125 X 2
'84 Aero 125 '84 Aero 125 X 2 '85 Aero 50
'85 Spree
odinxxix wrote:how cool is that! just imagine if that had a hopped up dio in it and took it to the drag strip.!
That is what this is for 72cc polini with 8.4:1 gears did a 13sec pass at the track. I have no doubt that if it had 9.8:1 gears it could be in the 12's easy.
Even the NQ50 goes too fast for a six year old
72cc polini with 8.4:1 gears did a 13sec pass at the track. I have no doubt that if it had 9.8:1 gears it could be in the 12's easy.
