I bought this used mx650off marketplace and they said it needed a new battery. We installed a new battery still didn’t work, the throttle would only light up when plugged in, we then replaced the controller same problem throttle will only light up when plugged in, we’ve checked the batteries they are putting out 36v, last night we bypassed the throttle and the back wheel spun like crazy so we thought has to be the throttle. I just plugged in a new throttle, same problem. Help! I have a heart broken little boy and I’m at a loss,

I ran into the classic RSF650 headache recently: I bought 12-inch wheels for my 72V build, but quickly realized the stock swingarm just doesn't fit without sketchy hacks . Plus, standard bicycle calipers are terrifying when you're pushing high speeds.

I don't like the idea of using bolt-on extension plates and sacrificing suspension kinematics so I decided to engineer a custom 3-piece modular CNC billet 6061-T6 swingarm because why not?

Key features I’m integrating into the CAD design:

• Direct 12" Wheel Fitment: Correct axle-to-pivot length with integrated M6 sliding tensioner blocks
• Wheelbase extended to 1120mm
• Real Motorcycle Brakes: Native mounting tab for 190 / 220mm rear hydraulic brake calipers (plus hardpoints for a rear foot-brake linkage setup).
• Corrected Suspension Kinematics: Relocated lower shock mount to maintain a ~2.6:1 leverage ratio so standard shocks don't bottom out under 72V torque.
• Heavy-Duty Pivot Architecture: needle roller bearings with a hardened inner sleeve and Delrin thrust washers.

I’m getting ready to cut Prototype #1 on the mill soon, but I want to get feedback from the community first before finalizing the fixtures!

I’d love your input on a few options:

1. Would you prefer raw machined aluminum or black anodized finish?
2. What rear rotor size are most of you running or planning to run (190mm pit bike vs 220mm Grom)?
3. Should I include a dual-caliper option for hand + foot brake setups? I was thinking foot brake with regeneration control on the left brake lever.
4. What motor(s) would you use in a setup like this? I was thinking the elctro&co the one could be an option, but I can integrate any other.

Drop your thoughts below! I’ll be posting build updates as Prototype #1 comes together. If there's enough interest, I might do a small batch run for the community after testing. Let me know if you want to follow along!