Zorge.

Actually there is not that much to tell about the conversion, it is all quite straightforward.
I did all the engine stuff at the same time. The BBR 150cc kit and cam is an off the shelf item sold for the Yamaha TTR125, same engine as the XTZ. So just dismantle and refit with no dramas. The Protork exhaust system can from Brazil, a neighbour of mine exports Chinese bikes to Brazil and he knows the owner of Protork, so I got a on off, looks like standard, exhaust system which is considerably better than stock. There were a couple of issues fitting ( maybe the Brazilian XTZs are a bit different to the Chinese ones ) anyway nothing that a bit of cutting, welding and repainting couldn’t solve. I also was able to swop the original carb that was useless at making power with a Mikuni TM24. It bolted right up except I needed a new throttle cable ( from a TTR125 ) and a sneaky mod to make the front of the carb slightly larger in diameter to fit like a glove in the inlet manifold. I bought a few different jets and after a bit of trial and error I have got it dialled in nicely.
Then came the cheapest engine mod, lighten the flywheel. The original is just so heavy. Not sure how much it weighs now but the motor revs up a lot easier.
I thought the Yamaha CDI was holding back the bike, so a programmable CDi and a bit more of trial and error made a big difference.
Must be ok as the original motor struggled up to 80 kph and now it flies straight up to the rev limit which gives about 105 kph. It could easily be geared for more speed but I prefer to have a bit more acceleration off road.
Probably the worst thing about the XTZ when I bought was the original suspension and tyres. Tyres are an easy fix, I started with Kenda K270 and now I am using Kenda K778s. Both of which I highly recommend and have the advantage of being so cheap on Taobao. A really good mate of mine that travels regularly to Australia sourced a complete front end from a 2003 YZ250. It was in near pristine condition, I learned how to rebuild the forks from a Youtube video and fitted new bushes and seals. To get the YZ triple tree on to the XTZ was not as straight forward, I had to get the centre shaft machined to the same size as the XTZ so that I could reuse the XTZ bearings. I made a mess of the fork oils, firstly I used an oil that was far too thick and I didnīt read the workshop manual about setting the oil height. Anyway that got fixed with some Torco RSF Light oils and a bit more reading, but the front was still too stiff. A pair of 0.37 Eibach springs sported that out, the front end is now excellent. I used the YZ250 from wheel which is about half the weight of the XTZ one and of course the YZ brakes with some EBC pads. At the same time I fitted a set of EBC rear shoes from a TTR125 and the rear now stops well.
I sourced from Ebay a brand new rear swingarm, shocker and pro link of a TTR125 which apart from being a lot lighter that the original soaks up the bumps as well as the front. Of course it wasn’t a straight fit, I had to make and weld some brackets for the prolink to mount to the frame and as the TTR125 uses a 16” rear wheel I had to get the swingarm extended by about 2,5 cm
For the winter I will be using the XTZ as is, it is now a fun off road bike with enough power to actually climb hills and to get out of its own way. The suspension and brakes are really nice.
It seems that there is always something else to be done with this bike, I am ok with that as I enjoy getting my hands dirty and working stuff out. At the moment I need to source a Speedo drive and cable from a Yamaha WR450 to get the original speedo working again and I really should take her down to a rolling road to see if my trial and error set up is ok.
Over the summer ( when it is too hot to ride down here ) I will probably do the Yamaha Zuma cylinder and head conversion. It basically all bolts up except for a couple of hacks. I nice build to do on the kitchen table when the misses is away. I’ll need a bigger card, maybe a Mikuni TM 28 or 30 and then a bit of trial and error to get it running right. Like that it would be a pretty decent fun off road bike.