My Vintage Honda Dirt Bike … Might Be Alive?

There are a few common tropes in the car-enthusiast sphere that I don’t subscribe to. It’s not that they are bad, or people shouldn’t do them—I just choose not to. My cars don’t have names, and I do not lean into the anthropomorphic ways in which some talk about project cars and other mechanical objects. Yet, in my darkest moments, I’ll resort to anything. This time, treating my cantankerous Honda XR600R project like a dog in need of training … well, it kind of helped.

I’ll pardon you for thinking, “Another column about the bike that won’t run? Why won’t this guy move on?” Honestly, that’s fair. I’ve thought the same thing several times during these last five weeks. I keep returning to the topic because I’m trying to learn from my mistakes: I was so bold as to think that starting and breaking in this engine was going to be simple, and I deserve the tuning issues that have cropped up.

The XR600R—otherwise known as the big, dumb bike of my dreams—is nothing more than a pile of parts stitched together with a surprising number of M6 bolts. Assembled by the book, there is nothing that should be stopping it from running as it should. Well, except for all the things I changed. This engine came to me in 14 boxes and, as I carefully built it up, I tweaked and changed things as I saw fit. New camshaft with a grind different than factory? Let’s do it. Big Keihin FCR41 carburetor? Who wouldn’t?

A smarter man, that’s who.

Diagnostics on a new-to-me project are tough enough, and learning the intricacies of particular care and feeding of this inanimate object was complex on a good day. Over the course of the engine rebuild, I took that system and changed various parts until I had no other option than to go all the way back to the very start of any diagnostic adventure: Fuel, air, and spark. I realized I had an air problem disguised as a fuel problem. For three weekends in a row, I fiddled with, removed, rebuilt, cleaned, re-cleaned, stared at, cursed at, and finally tore apart the FCR carb a third time to find out why a device designed to so carefully blend air and fuel was putting in a couple extra spoonfuls of air.

I could get the big thumper to run with the mixture screw back out significantly further than recommended, essentially adding as much fuel as the pilot jet would flow. Even then the engine would cough and backfire through the carb as if it were running crazy lean. After double- and triple-checking all vacuum-leak possibilities and even making a custom O-ring for the carb, it took plugging the hot-start mechanism with silicone to finally make the carb meter the air properly. The whole dance got frustrating enough that, in the depths of the cold and gray that descends on the northern states every February, I finally gave in and started talking to the bike as if it could hear me. Coaxing turned to begging, as if the engine would communicate what it wanted or needed.

When it didn’t respond, I shoved the whole half-assembled motorcycle in the corner of the garage and did my best to wipe my brain of the problem. Then I resorted to a curious theory. Sometimes in a training class, when faced with a stubborn dog, the instructors bring in an example. I needed an older pup that talked the same language as the XR600R and was already on my side. So I popped over to a friend’s house and borrowed his well-trained Honda XR200R. I put it on the lift, fiddled with it for a bit, and got it running right after a basic tune-up. The whole time, I glanced at the XR600R as if to say, “This could be you. Just look at how it gets to play up and down the driveway, and even lap the neighborhood, regardless of weather—all because it chooses to work with me, not against me.”

The most painful part of this absurdity? It worked. After leaving the 600 in the corner, untouched, for a full week, I regained the motivation to try again. I went through the starting procedure: Rotate the engine carefully to top dead center(TDC) on the compression stroke, use the compression release to knock the piston past TDC, reset the kickstarter, and kick it like you mean it.

On the third try, the engine took the pace my right leg put into it, inhaling through the flat-slide carb, lighting the fuel on fire, and pumping out hot exhaust. It idled, high but steady. After 10 seconds, I clicked in the choke, closing off the additional fuel for cold starts and dropping the engine to a lower, smooth idle. The hearty thump from the pipe sounded so strong, yet so fragile. Before that day, the bike had never idled correctly. Even in the moment of triumph, I was plagued by doubt—was everything actually correct?

Who knows. Without some additional testing, I’m still not sure exactly which part of the plan was the silver bullet—and there comes a point where I almost don’t care why the plan worked. I did the final two changes (sealing off the hot start and adjusting the fuel screw) at the same time, in the always-a-bad-idea, shotgun approach, leaving me to wonder which worked and which was a placebo.

The engine runs now, though, and I can start thinking about pulling this engine back out of the frame and getting started on finishes and final assembly. Spring is right around the corner, and it would be great to get in a few test miles ahead of schedule. From where I stand now, this feels like the tallest peak I might have to climb. But I also thought this engine was just a pile of parts that, if assembled properly, was certainly going to work. No, this bike is proving to have more character than that.