Originally Posted by BadBMWBrad
I submit that your electronic ignition's spark-advance function is unreliable. This would explain engine overheating, poor fuel economy and sudden increase/decrease in engine power. If the spark timing does not advance at high RPM then the spark occurs too late for efficient fuel:air combustion. Much of the fuel:air combustion occurs late in the power stroke and the engine will over-heat. Fuel economy will also be poor. If the spark timing advanced intermittently then sudden increased/decreased engine performance would be manifest.
That actually makes a lot of good sense, and at this point, it seems like a great explanation as our other attempts to troubleshoot the problem have come to naught. We'd been planning to install a PowerArc ignition at some point, anyway - it's on our list of mods before a RTW. We've been planning to contact IMWA about the issue (just waiting until we get our 10,000km service wrapped up and check to see whether we're still having intermittent problems afterward) so I guess now our decision has to be whether we want to contact IMWA anyway and let them deal with the ignition under warranty (if they agree that it's the likely explanation for our problem), or just go ahead and install the PowerArc and see if that fixes the issue. I think I'm inclined to let IMWA sort it out and get it running properly before switching to the PowerArc, just in case there are any other underlying issues that are contributing to our performance problems. It's probably better not to introduce another variable at this point.
(We started the 10,000km service on Sunday - worked on the bike for about 6.5 hours and got most of it wrapped up, now we're just down to lubricating various things and tightening all fasteners, which I'm hoping we'll get to tonight. And then we need to take it out for a test ride to see how it's running! We did find that the valves were out of spec - all had loosened - I think they were about the same as the first time we did valves. But the dealers we spoke with said it seemed unlikely that valves were the issue. I guess we'll see now that we've adjusted them and re-synced the carbs!)
We've got most of the wrap-up stuff written - Kay did a lot of the writing and I just need to add my notes to a few of the pieces, like our thoughts on the Ural. I'm *hoping* we'll get to post that stuff tonight, but if not, it'll be Thursday for sure. Then if anyone has any questions about specific kit, etc. we'll address those. And of course, the story won't be complete until we diagnose our mysterious performance quirks, so we'll post whatever the resolution turns out to be once we've got that figured out!
(But yes, I'm very happy with the Ural's performance otherwise. It didn't do any of the stuff that people would lead you to think about the Ural being unreliable. It's very simple to work on, even on the road, and no catastrophic failures - it ran even in the 100+ degree heat and even when we were flogging it all day!)