I have found an auction from JT's motorcycles on eBay UK, and it says: "YAMAHA RD200 DX / YCS1 / YB125 / YB200 38 TOOTH REAR SPROCKET (REPLICA)". I konw that the same models of 200 DX uses the correct sprocket, but I'm unsure about this one. It seems the part number is 836-38. Here's the auction: http://www.ebay.co.u...=item19ce66b299

It has the correct sprocket in the bottom left in the picture, but it's of course only an example. The annoying thing is that I tried to send a question to JT, but they're not open for that on eBay. Even though the auction says:

TO ENSURE CORRECT PARTS ARE SUPPLIED, PLEASE SUPPLY AS MUCH INFORMATION AS POSSIBLE ABOUT YOUR BIKE I.E. MODEL / FRAME NO. / YEAR.

Right. That's easy when it's impossible to ask questions! So does anybody know if this fits the RD 125 DX?

check out JTS,s own catalogue

http://www.jtsprockets.com/catalogue

Thanks! Found it. Turns out I need 837, not 836. Back to the hunt, then.