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The American Motorcyclist Association Posted February 24, 2006 |
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Project F, Part 6: Work in progressby James Holter Sometimes, things don’t go as planned. As those readers who followed the journey of my 1981 Yamaha XT250 from the edge of a garbage dumpster to snazzy rat bike know, a little paint, lots of time and a few bucks can make anything look stylish. (See “Project F: From Dumpster Debris to Beginner Trail Bike.”) Indeed, even if I say so myself, the XT looked clean, felt tight and oozed a certain ’70s charm that would earn anyone riding it instant trail cred. But that was before I went and screwed everything up. You see, I actually tried to ride the thing. The XT’s first real venture back out onto the trails (at the Hocking Riders ORV Park in Logan, Ohio) started out well enough. The little four-stroke fired right up and happily chugged around the parking area as AMA Senior Art Director Denny Lee Thrush and AMA Photographer Bill Andrews and I contemplated which trail we would attack first. After talking things over a bit with park owner Scott Lyon, who took time out of his busy day to let us in, we decided to follow a relatively easy two-track trail around the perimeter of the property. Then off we rode, Denny on his KLX300; me on my CR250; and B.A., long-time “Harley guy” and dirtbiking beginner, on the XT. About this time, I was feeling pretty smug. First of all, the weather was perfect—mid-50s and sunny. Despite several delays, Project F appeared to have scooted just under the annual deadline for prime riding weather. Second, it looked like the XT was ready to put in a solid day on the trails, confirming my mechanical skills with a successful run. Third, I was on the verge of introducing B.A. to the awesome world of off-road and possibly planting the seeds of conversion in an exclusive street-rider. Expectations, crushed Unfortunately, the lasting nature of first impressions is only surpassed by their unreliability. It was maybe 300 yards down the trail when the first signs of what would manifest as a monumental failure started to emerge. I looked over my shoulder and B.A. and Denny were no where to be seen. My first thought was B.A. caught a slick log at a funny angle and went down, breaking his leg on a fat rock. Considering this ride was jammed into B.A.’s schedule a few days before he and his better half, Star, were taking a trip to sunny Florida, my mind was well into the second dozen ways Star would exact her revenge when I came up on B.A. and Denny trying to start the XT. The owner of a 1975 Sportster, among others, B.A. is no stranger to kick-starting motorcycles, and he was giving the XT his all. But, unfortunately, it appeared a whole lot of calories were being burnt up for no good reason. The XT wasn’t cooperating. After a few more attempts on B.A.’s part, I decided to take over kicking duties. Suspecting the XT might be running a bit cold-blooded, I flipped on the choke and the XT was once again chugging away after a couple more solid kicks. Well, that’s settled, I thought. The bike’s simply running lean, a condition made worse by the cooler weather. It was a lot warmer earlier that year when I first fired up the XT, and it even needed a bit of choke then to idle more than several seconds. I handed B.A. back the bike, yelled something about giving it plenty of throttle and got back on my CR. We continued down the trail but—you guessed it—the XT had no interest in making this easy for B.A. It ran horribly and died again. Again, I rode back and helped start the bike. And, again, it died after another minute or so. We cycled through this process a couple more times. Each time, the bike would die on B.A. and I would have to start it. At one point, I took the XT for a short ride through a small clearing. The XT didn’t cut out and, I told myself, didn’t exhibit anything other than some slight lean tendencies that were bearable until I could mess with the jetting. Even though it went against my better judgment and I couldn’t put a finger on exactly what it might be, I wrote the earlier stalling off as some unconscious element to the technique of riding a dirtbike—properly slipping the clutch, applying the throttle, whatever—that B.A. had not yet developed. Maybe all those years on big twins ingrained some obscure riding habit that just didn’t jive with this small-bore single cylinder dirtbike, I rationalized. With no better answer, I figured B.A. would “get it” soon enough and we could enjoy our day. We headed back out of the clearing and it soon became painfully clear that the XT’s poor running had absolutely nothing to do with B.A. and everything to do with me. “We were just riding along, and then there was this loud clank,” B.A. said and Denny confirmed when I back-tracked to assist with the XT for the hundredth time. “It backfired and died. And, it won’t start again. And, for some reason it seems harder to kick.” I took the bike from B.A. and tried to start it. This time, I got nothing, not even a cough. First step: check the spark. No spark. Denny had an extra plug. Nope, didn’t work. Fine, there’s a lose connection somewhere, I figured. There was this one that kept giving me fits during the rebuild process—that’s it. Again…nope. At this point, we gave up trying to do anything on the trail. Obviously, the electrical system was at fault here. We decided to tow the XT to the truck and work on it there. After finally getting back—Denny only flipped his KLX three or four times while towing me on the XT while B.A. rode my CR—we started tracing back through the electrics all the way to the stator plate where my ineptitude slapped me right in the face. The fasteners securing the stator plate to the cases had backed out. The flywheel magnets had stuck to the coils on the stator plate, and each time we tried to start the XT, the magnets dragged against the coil surfaces. No wonder it was harder to kick! This, I finally capitulated, was not going to be a successful ride.
What went wrong Obviously, something very bad happened when the stator plate came loose. The evidence strongly suggested that one or more of the coils on the stator plate was damaged when they were smacked by the rotating flywheel. There are basically five parts to a CDI-based electrical system: 1) the charging (or source) coil, 2) the pulser (or pick-up) coil, 3) the CDI box, and 4) the ignition coil, which is what plugs into the fifth part, the spark plug. Basically, the charging coil builds up the juice, the ignition coil stores it, the pulser coil says when to release it, and the spark plug delivers the goods. The CDI box is the brains of the bunch and keeps everything else in line. The spark plug is easy and cheap enough to just replace. The other pieces—particularly for an old bike like the XT—can be individually expensive to the point of literally “totaling” an otherwise fine running bike. Although it had to be done, I was not looking forward to finding out what was busted on the XT. I grabbed my multimeter and got started. Although I didn’t suspect it would have been damaged, I began with the ignition coil. With the spark plug cap, it checked to about 17k ohms, without it checked to about 6k ohms. That was all within spec, according to the service data sheet that I downloaded off Yamaha’s website. Next, I moved to the coils on the stator plate. These can be checked through the wires that run up to the CDI box. I stuck the multimeter on the brown and red wires to check the charging coil. The reading was just under 500 ohms. All looked good. Then, I pulled the grey-red and white-green wires for the pulser coil. I got a reading of about 20 ohms. It needed to be within 10% of 215 ohms. Bingo! Assuming the CDI box was OK—a unit that most part-time mechanics like myself can only diagnose as the problem by eliminating everything else—then I would just have to replace this tiny black box that bolts to the outside edge of the stator plate and the XT would be back on the trail. Unfortunately, though, pulser coils for these old bikes are apparently rare commodities—and run more than $130 directly from Yamaha. It took me some time before I found one that was reasonably priced (I bought a complete stator plate for another year XT for about $10 off an online auction website). Even then, the connections were different and the “new” pulser coil had to be soldered into the old wires (covered with shrink tubing for protection). The spark? Blue and fat. The number of kicks to start the XT? About four. The relief of delaying failure? No, not priceless, but definitely worth 10 bucks. Take II B.A. was a great sport about the whole mess. Even though it was my bike that broke and I drove, he did invest a perfectly good riding day into this fiasco. He could have been out taming some pavement on his Low Rider, but instead was stuck holding down the tailgate on my pick-up truck. Still, he insists he wants to give the whole off-road thing another go. The XT will be waiting. I even since solved the lean condition—which is another column. But, more important, I reminded myself that older bikes, no matter how meticulously rebuilt (and the XT was not), are a work in progress. Heck, even when new, these bikes needed more attention than modern machines—and that’s certainly the case when they’re 25 years old. But if you’re as screwed up as some of us, that just means they’re 25 times as fun.
Project F,
Part 1: Bringing a "free" 24-year-old XT250 back to life © 2006, American Motorcyclist Association |
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