Dirt Rider - 2001 Honda CR80R During the Build
The current backyard mini craze started with XR80/100R engines transplanted into two-stroke 80cc motocross chassis'. As amazing as it seems, there are at least two good reasons to replace a modern, powerful, reliable 85cc two-stroke engine with a larger, heavier and somewhat antiquated four-stroke one. The first reason is that adults racing or play-racing on smallish four-strokes are having more fun than humans should be allowed, and how do you put a price tag on having fun and recapturing your youth? A side benefit of all the small-bike/adult craziness is that advanced riders who have outgrown the crude stock suspension of their entry-level trail machine now have options other than switching to a race-bred two-stroke.
We'll concede that most modified four-stroke minicycles end up at backyard, home-brewed tracks, but there are organized races as well. For years there was an understood class limit of 150cc for the bikes that used two-stroke chassis. That rule made sense since the outer limit for the Honda XR100R engine was 150cc. Now there are a lot more engine options and combinations, so the rules, for events sophisticated enough to have rules, usually say that any air-cooled, two-valve engine is fair game. Most conversions are based on Yamaha TT-R125 and Honda CRF150F engines, but the cheaper and more plentiful XR200R engine recommended by Dave Miller of DMC is a known quantity with great aftermarket support.
A custom four-stroke mini was a perfect EBay project. The only way to build one is to start with two perfectly good motorcycles, and after a lot of time and money end up with only one and a pile of extra parts. Despite the headline used here, there is no such bike as a Honda CRF200X, but there should be, and there is no good reason we can see why Honda (or any manufacturer) refuses to build one. That's another reason we chose to build this bike. The vast majority of the bike shown here is straight production Honda. Honda builds not one, but three engines that bolt right in this DMC-modified CR80/85R chassis: CRF150F, XR/XL200R, and CRF230F. The suspension, brakes, wheels and body parts are all production CR80/85R fare. This bike has a Thumper Racing 2mm oversize big-bore kit with a Wiseco high compression piston (still under 200cc total), but the engine could easily have been left stock. The hand of the aftermarket is heavy in places, though. The DMC frame modifications require 42 laser-cut parts and brackets and seven feet of chrome-moly tubing! The exhaust pipe and intake manifold are special limited production items from DMC included in the frame kit's $1999 price.
Finding a proper CR80 or 85R Expert donor bike was easy, but finding one cheap enough to justify the shipping wasn't. Finally a clean 2001 showed up within driving distance, and we bid high enough to ensure we'd end up with it, but there weren't other bids, so we got it for $1600 with the original tires still fitted and in good condition. It didn't come home with us, though; it went straight to DMC to have the frame modified. Starting with a new frame (no numbers) rather than one with a clean title is too much of a paperwork nightmare. If you desire to start with a new frame, all states have a process in place that allows for frame changes. Buy a new frame, and then take it to the proper authority to have the official frame numbers stamped or riveted on. In California the Highway Patrol does the VIN inspection. You'll need to do the same thing after the new engine is installed, so if you have the engine to take at the same time, you might save a second trip.
We got the completed frame kit and all the stock parts back from DMC before we were able to locate a suitable XR200. We saw many at reasonable prices, but they were on the wrong side of the country. The shipping costs made them undesirable. Then we located a clean 1990 owned and ridden by a woman, but mostly parked for the last 10 years. $1800 was more than we wanted to pay, but with shipping it would cost nearly the same for a much harder-used example. We pulled the engine and took off the top end to check it out. EBay allowed some donations to the project, but limited them, but we were allowed to use things we had around. We remembered that there was a shipping-damaged (a chipped fin) Thumper Racing 2mm oversize XR200R cylinder and Wiseco high compression piston stashed in the garage. There were even gaskets, so we were able to button the engine back up the same day. The carburetor was pretty gummed up from sitting, so we replaced the pilot and main jet and cleaned it up a bit. The tappet clearance was a bit loose, so we adjusted those, drained the oil and got ready to roll on.
DMC engineered the frame well, and the engine and all the other parts fit up fairly easily. The bike didn't run correctly, and Dirt Rider's new editor Jimmy Lewis correctly diagnosed and remedied a plugged carburetor air passage. We had a few small issues to deal with once we rode the bike. It was very hard to kickstart, but the XR donor bike came with the original manual. It detailed adjusting the automatic decompressor cable, and once that was done it started very easily. Also, the exhaust pipe is very close to the cable, so we insulated the pipe and the cable with a section cut from a high-temp spark plug boot cover from PAW. A radiator no longer supports the right side shroud, and an aggressive rider squeezes hard enough with his knees to push the tip of the shroud in far enough for it to interfere with the fork. We bought some Works Connection frame guards on EBay, and they had come with a radiator guard plate that we had consigned to the spare parts bin. We dug it out, installed it between the tank mount and the lower shroud brace. Voila! No more problem. All that was left was to install the new graphics and fresh Bridgestone 401/402 tires and make a quieter muffler/spark arrestor. We modified a used FMF spark arrestor for a Kawasaki KX250 to fit the DMC header. That made us spark and sound legal to ride off-road in California. The torch-welded joints looked completely disgusting, and we were embarrassed by them until learning that we welded aluminized carbon steel to stainless steel with a torch and normal welding rod. Supposedly that can't be done, but so far it is holding up fine. We hope to have something custom from FMF installed before the bike is auctioned off.
Getting the air filter element and cage mounted takes some patience, but otherwise we are very happy with our bike so far. Small and light riders love it on the track or on the trail. It likes berms better than flat, slippery turns, but it turns well enough. It shines in fast sand washes and handles better through whoops than the stock CR80R did. Dirt Rider's Cory Neuer raced the Ebay special at the infamous Langtown backyard minibike supercross. The bike holeshot every start and ended up second in the amateur class. Neuer is 5'11" and 160 pounds, and the bike worked fine for him, and it worked for our 5'3" 120-ish women trail riders as well.
Now if we could just come up with the money to buy it for ourselves.