I've added 70cc kit and a MRP performance pipe to my R50x and wanted to post a brief review.
I added the Malossi cast-iron 70cc cylinder kit (part number 31.8723, 10mm pin). Also added is the MRP R50x racing exhaust (part number N-MP-02059). For reasons explained below, I simply drilled out the main jet to up-jet it--so I can't provide you with an exact size for the jet. But know that up-jetting is necessary.
Completely stock, with the restrictor, I was topping out at 38 mph (according to the speedo, which we all know is inaccurate). After these modifications, I'm topping out at 56 mph. In addition, the torque is substantially better; improving acceleration and hill climbing.
A couple notes about the pipe: this pipe is loud. You have been warned. Also, the pipe has a glossy coating on it. I've put on approximately 300 miles since installing it and I've noticed that close to the engine's exhaust port, the coating is starting to peel off, as well as become discolored. I suspect this is a result of the heat, which is inevitable for an exhaust pipe. I would have though MRP would anticipate this.
These mods turn the R50x into a whole new animal and I would highly recommend them. I got my parts through Oilyhands and I would highly recommend working with him. He was helpful, knowledgeable and responsive. MRP's first shipment didn't contain the jets that I ordered. Oilyhands worked with them to resend the jets, which they did. But they then sent the wrong jets, which is the reason I ended up just drilling out the stock jet. Two separate scoot shops in my area have confirmed that just about every order they make from MRP has some kind of error in it, so I'm confident the error was not Oilyhand's. (MRP seems like an overall good company, but has some problem with shipping). Regardless, ordering through Oilyhands was a positive experience.
Since ordering from him, he has started a website. Although I did not use the website, working with him was such a positive experience, I will nonetheless post a link to the site:
http://whidbeyislandmoped.com/cart/Now that the weather is warming up, I intend on tuning my R50x some more and I'll let you guys know how it goes. On a separate note, since adding the cylinder kit, the in-dash clock does keep very good time and the turn signal timing is a little off. I haven't really invested much time in investigating it, but wondered if you guys had any thoughts?