The project so far: Zac’s gathered a load of parts, and started bolting them on to his DR650.
Last time I talked about my DR650 project bike, I said I had the bike re-assembled, but that it wouldn’t start. It’s taken a bit of time to chase the problem down, partly due to interruptions; I renovated my shed to double my shop space, which took time away from motorcycle projects. I also had to do some work on the ’96 RF900R to make sure it was reliable this year. And then, in May, my neighbourhood flooded so badly that I had to canoe into my shop to get tools. I got the 650 out before the flood hit my yard, but that set my plans back considerably.
The other reason it took so long to get the bike going was that I was at a loss as to why it wouldn’t start. I had a sticky float bowl in the carb, and while I thought the bike should at least run half-heartedly, I rebuilt the TM40 pumper carb, thinking that might be the issue. Nope, no luck. I wondered if it was the battery, thinking maybe I’d just gotten a bad battery, even though I’d just purchased it. However, this wasn’t the problem either. Then I wondered if the valves were too tight; I checked them, and if anything, they were too loose. I wondered if I didn’t have spark, so I checked the spark plugs and the ignition connections in the wiring loom; all seemed OK there.
So when you have fuel, air and spark and the bike won’t run, what is the problem? Either you’re not getting enough of one of those factors, or it isn’t coming at the right time. Could I have gotten the cam out of time with the crank when I reassembled the engine? I thought it was very unlikely, as I’d been super-careful to avoid that problem when I put the top end together. But I was out of other options to check, and just before I sat down to disassemble the engine again, I asked myself if any of the aftermarket parts I’d added in the rebuild would let the engine turn over, but would stop it from running?
The answer: the pulse coil, which is part of the aftermarket stator assembly I’d added. The DR650’s stock pulse coil is one of the bike’s weak points, and a bit of digging showed the aftermarket replacements were also potential problems, delivering weak, erratic or mistimed spark. But, it was hardly a common problem. I popped off the magneto cover and re-installed the stock stator as a Hail Mary move, one last wild attempt to see if the engine would fire back to life.
After bolting in the old stator, the engine immediately fired to life with the first press of the button.
So, while one of the big aims of this rebuild was to add more electrical output, which in turn would make it easier to add more lighting and heated gear, it turns out I’ll have to wait on that. I need to figure out what went wrong with the aftermarket pulse coil before swapping it back in.
So, I’ve had a few runs around town and in the woods with the rebuilt engine, and I’m mostly impressed. The top end of the rev range doesn’t feel any different from before, but it feels there’s more low-to-mid-range output, which is what I wanted for trails and back road riding, and why I went with Web’s 223 grind cam instead of the more popular 190 grind (which offers more top-end performance).
To be clear, this is all just seat-of-the-pants comparison, as I haven’t dyno’d it. It still doesn’t have the arm-pulling torque of a 2-stroke, but it does have plenty of grunt, and seems to pick up a bit more torque every time I take it out and the engine breaks in.
There are still some things to tweak; the valves sound a bit loose, and I think they could use another look. The throttle cable is still sloppy, and I’m not sure why. I suspect a careful tuning of the Mikuni TM40 carburetor after a dyno run might make the engine run a little better at the top end; it seems down on highway speed just a tad, but that could be a function of the break-in process. However, considering I never changed any settings on the carb during this process, I’m impressed at how well everything works. There’s even less backfiring than before.
Speaking of which, that new Leo Vince exhaust I installed has proven to live up to its recommendation. It’s lighter than stock, but without the obnoxious bite of the FMF unit I previously had on the bike. CMG readers know I dislike loud pipes, and while this bike never had the growl of a big-bore cruiser when I ran it with the FMF, it was still too much for cities and towns, so the new Leo Vince is the perfect compromise. If it’s legal for the EU streets, you know it’s got a reasonable sound output. The Euros keep a pretty close eye on that stuff.
I haven’t put the new Barnett clutch to a real test yet—no muddy rides, no mad wheelies. Yet. But I do find the pull isn’t as bad as advertised; some users end up only switching out half the aftermarket clutch springs, leaving two stockers in place to keep clutch pull lower. However, I find the clutch is perfectly usable with the entire aftermarket assembly in place.
The new seat from Seat Concepts is also proving to be amazingly comfortable, a huge upgrade over the stock unit and even significantly better than the Corbin I ran for years. However, I’ve only had a short time on this new seat, so I’ll reserve final judgment until I’ve had a few proper days in the saddle.
Overall, I’m extremely chuffed at how fun this bike has been to ride in the past few days. Off-road, it’s proving to be even better-handling than I remember; that’s partly due to the Ricor suspension I installed years ago, but also because the engine’s revised power delivery really does seem to match the sort of sensible throttle management you need off-road with a big bush pig like the DR650.
The biggest question is, how long will it hold together? Hopefully, even as my Mister Mom workload increases over the summer, I’ll get a chance to put the big Six-Fiddy through its paces and see if my mods were worth the trouble … and if the bike doesn’t blow up, there might be one more final round of additions yet. I still need to figure out that pulse coil problem so I can add more lights!