Built a WR200, because I didn't know they existed

Midway through building a desert bike, I had an idea get into my head, and it wouldn't get out. It was a woods bike. A modern chassis with a small two stroke motor. I put the idea on hold while I finished the CB, but months later the CB was mostly done and the idea never stopped itching.

No problem, right? Go buy a KTM 200. Only problem is they vibrate too much. Too much for me anyway. Ok, so buy a '98 Gasgas ec300. Those have a counterbalanced motor and are really smooth. Only problem is finding one. So, I'll have to build one. And this one's going to be built a lot faster than the CB was, for the sake of my sanity.


I had a 1999 YZ 125 that was a nice light bike, but the motor was awful for trail riding. The first idea for a donor motor was a Gasgas 300 quad. It's the same motor as the ec dirt bike, but they kept the counterbalancer for a lot more years. Still hard to find, and couple I saw were expensive. For some reason it took me a while to figure out that pretty much all quad motors are balanced. That opened up a lot of options. In the end, the Yamaha Blaster was the donor. It's a 200cc two stroke, counterbalanced, air cooled motor. It was built pretty much unchanged from 1988 to 200something, so parts are easy to get. As a bonus, it's also a Yamaha which I figured would make matching things up easier. [Spoiler: it did.]


Midway though researching this, I discovered that Yamaha did build this. It's the WR200, and imported to the US in '93 or '94. It lost a magazine review against the KDX200, and that was it. The major differences to what I built are that the factory bike was watercooled, more powerful, and heavier.


I didn't take pictures while building, I was too fixated on just doing. So here are the results.

So the first big question is, does the motor fit?

The answer is: it does now.

There are three motor mounts on both the YZ and Blaster motor, I'm using two of them. The swingarm pivot and the front motor mount are exactly the same distance apart.

The rear motor mount is both smaller in diameter and width on the Blaster than the YZ. So I drilled the hole out to 17mm from 16mm. Shims took up the width. The Blaster motor needed to be installed 1mm to the right to get the chain lined up right, so the shims aren't the same width.




The front mount was the right diameter, but was too wide. So I cut the cases down with an angle grinder. Like the rear, not quite symmetric, but close.

The pipe came together thanks to a lot of help from Rick and Alex. I took the FMF expansion chamber from the Blaster and cut it up, rotated the sections, and re-welded them to get about the same tuning while fitting the YZ frame. This job kept six hands very busy.

The end of the expansion chamber was from the original YZ pipe, and the muffler was an aftermarket spark arrestor meant for a YZ125.

The intake was also a bit tricky. There's no way the YZ carb is fitting (way too big). The Blaster carb sits at the wrong angle to go to the YZ airbox, so I replaced the, um, whateveryoucallit, adapter.

First attempt, it seemed a bit restrictive. The bike topped out at around 40mph with this.


It's just a pre-bent section of exhaust tubing cut and welded to a flat plate which bolts on to the airbox.

Version 1.5, with the bend widened up for more airflow. Now it goes a little over 50. Since gearingcommander says that it will hit the rev limiter at 60 that's probably as good as it's getting. Stock, the motor is claimed to make 17 hp.

One of the side benefits of the air cooled motor is that there are no radiators to get in the way of the forks. So I cut down the steering stops to get a little tighter turning.




This was a full u-turn with the bike upright. The board marked where the bike turned before the stops were filed.


From 12.5' to 11'. By comparison my TE250 turns in 13'; it's steering is limited by the steering damper. If I do put a damper on this bike it will have to use a linkage.

The gas tank is the stock tank from an XR400. The YZ tank doesn't work, it hits the cooling fins. The XR petcock needs to be mounted backwards so the fuel line doesn't hit the frame. I'll replace it soon with a forward outlet.

So that's about it. Only other thing to mention is that the rear wheel is from a WR250F. It's about the same, but 18" instead of 19", so I can fit a trials tire. Also, the brake rotor is slightly larger on the WR, and rubs something in the YZ caliper. The YZ brake is good enough, though.

The only other thing I need to do is make a skidplate. That and ride it. I've done a few rides on it and the motor works great in it. Much better than the 125. The suspension was rough, being tuned for a motocross track. It's been revalved and resprung, but I haven't gotten a real ride on it yet to see how it works.

I have the same idea for a nice light cheap bike, only mine will be street legal.

What is the finished weight, is it lighter then a kdx 220?

I was thinking along the lines of a xt 225 engine in a yz 125 frame.

so a little heavier but with e start.

I suspect it's lighter. Hard to say without weighing them on the same scales. I was going to weigh it yesterday, but couldn't find both scales.

The Blaster motor with oil is 5 pounds heavier than the yz motor with oil and radiators and coolant. 50 vs. 45 pounds. Guess another 5-10 pounds for the heavier rear wheel, sidestand, tank bracket and skid plate. So the 'claimed dry weight' should be the 193 of the YZ + 15 pounds, or 208#. Compared to 222# for the KDX.


Unfortunately street legal is not happening in this state with a modern Japanese MX VIN.

Awesome Luke! I started working on my XR250/CRF conversion again after selling my KTM. Back to basics.

Great! I rode a friend's xr250 a little while ago, what a nice motor.

Awesome. I have a warmed over Blaster with no paperwork and a 1972 Honda SL125 with a basketcase motor. Was planning on smashing the two together and you just cemented it. Way to go on this one.

Very Cool!

Should be a nice woods bike. I'd love to update my old IT200 to YZ suspension and brakes. The IT motor is basically the same as a blaster.

How is the transmission gear spacing? Wide ratio or tight like a motocrosser?

Just my .02 (if it's worth that) but why not weld in new mounts for the front instead of cutting the case down?

Like others, I am liking the idea of a xr250 in a crf frame. If built as a custom with all legal bits on, it would be issued a new VIN as a street legal bike here in NM

I've been thinking about doing something similiar, like dropping a DRZ-250 motor (electric start) into a RM250 chassis that I already own.

That poor little bike isn't going to know what hit it.


Post pictures.

I bet that'd be good. A front end swap should be pretty simple. Just a warning, the YZ suspension is pretty brutal in stock form. You might go for WR parts instead.

The transmission is really wide. It's geared for about 50mph on the top, in theory should hit the rev limiter at 60. In 1st it will putt along right at 2mph without slipping the clutch.


I cut the case because it seemed like a good idea at the time. I think my reasoning was that I had already ruined the cases by drilling out the swingarm pivot hole, so if things didn't work out I wouldn't have also ruined the YZ frame.

In retrospect, I should have cut and replaced the mounts. That would also allow the motor to be lowered a bit at the front which would give some more room between the carb and the shock.

But you needed it done now, and cutting and welding was more time! (Or, at least, it sounded like more time and work when you were trying to fit the engine in there) :loll

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