XR Supermoto

In 2010, I sold a 2003 CRF150 for 1300 bucks. The girl I sold it to paid me in 20’s — the most money I’d ever seen in cash. I bought a 1999 XR250R with it and grew my love of motorcycles on it for the next five years. A supermoto project has always been something on my list and the XR sitting in the shed was begging for a revival. The XR isn’t a popular Sumo base because of the clumsy suspension and the poor power-to-weight ratio, but the pluses made sense to me: bulletproof engine that would hold up to highway abuse, good gas mileage, and I had one rotting in a shed.

The project started out life as a muddy jumble of parts I had shoved into the back of my Subaru:

Several things were on the list for the Sumo conversion: upgraded front brakes, sumo wheels and tires, all the lights and wiring to be street legal, an upgrade to a 32mm flatside carb, and eventually a 280 overbore. I got a few of them done.

Sumo wheel kits are wicked expensive, but it’s really not that bad if you do it yourself. I had never built a wheel before, but YouTube confidence struck again and I decided to go for it. While I was in Japan I fell in love with the idea of a retro gold anodized rim, and found a company that made them in the size I needed. Warp Nine racing pullin’ through with the 17″ x 4.5″

I opted to use the OEM hubs originally on the bike. After some confusion, I got the dudes at Buchanon spokes to cut a custom set to lace the wheel with.

Turns out it isn’t that hard. After a few tries I got the lacing pattern correct, and after that it’s just a matter of getting everything tight and true — slow, but not difficult. I didn’t have a truing stand so I improvised.

I shod the wheels with Diablo Rossi IIs, which the boys at South Bound Honda mounted up for me. The last time I mounted a large motorcycle time myself was a little jarring and I was worried about marring the new gold rim sickness.

Here’s the chassis with the finished wheels mounted up for a gander:

I had planned on this being my project to occupy the spare time I couldn’t spend climbing in the winter, but after seeing the wheels on the bike I couldn’t stop myself. In a sleepless 30 hour binge I got most of the work done for it to be rideable. I cleaned everything on the bike, wired a custom headlight, blinkers, and tailight, and rebuilt the front suspension (with a ghetto shock preload for road use — a USD conversion is in the works.)

Here it was fully mocked up, but not quite road ready:

I was only waiting on a few more bits from the mail at this point — I had to order a chainwheel in a custom size to get the gearing correct, and the Mikuni 32mm flatside carb was late in the mail. But they arrived! Here is it is more or less finished, with the oversized front rotor, proper gearing, new chain, and a very maladjusted carb.

After getting the jetting dialed in, the flatside carb gave up a noticeable performance increase. It’s bigger, so more fuel and air get shoved into the chamber, and the flatside supposedly results in better fuel atomization. I was hesitant, but I’m pretty sold on it now.

A few more things to do to get it fully dialed in, but that’s mostly it!

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