At the end of the previous post on the old girl or about 500km ago, if that's how you want to measure time, I was pretty convinced that a rejet would be the ticket to find the missing horses in the XT's engine. But first I had to find the poor electrons and a bit of magic smoke that attempted to escape the old girl's wiring loom. As most of the electrics had fallen silent, I assumed that the capacitor I use as a battery replacement had called it quits. So this time I upgraded from a 4700µF to a 47000µF/25V capacitor, also with the intention of making the indicators work at idle and giving the regulator a bit of an easier time.
Initially I ordered two caps, but the second one was a 47000µF at 63V and about the size of a pint glass - makes a good conversation piece or paperweight.
I'll spare you the gory details, but in the end it turned out to be a massive short that involved the switched 12V power source from the ignition barrel and the ground coming from the neutral switch. During testing I suspected the regulator to be behind the whole issue (assuming some sort of internal short), so I built this beautiful setup for testing.
As that didn't reveal anything (why should it this part was working just fine), I used an old bilux bulb as a dummy load between the alternator's two phases to see if they still put out anything.
It works significantly better, if you actuall plug the bulb into the one coming from the alternator and not the one from the regulator. (Did I mention I did a college for micro-electronics... yeah, time well spent. 😉 )
Somewhere around this time I worked out that as soon I unplugged the neutral switch the fuse would continue to work, so I called it "good enough" for now. Keeping in mind that finding those elusive ponies was a process that went on for several weeks, I tackled quite a few jobs along the way. One was that the joint between headers and exhaust can would constantly leak and chew the graphite gaskets. It turned out that if one sliced up a bit 44.5mm exhaust tube and shoved it over header that would completely eliminate the need for said gasket. (18 Euros a piece...)
As the stock 43F-muffler is in a bit of a state (and there's something rattling around inside of it), I was pretty convinced that one of the internal baffles had fallen over and thus was blocking the exhaust. But then there was also this lovely Arrow Paris-Dakar replica exhaust. Full stainless, freshly repacked, but unfortunately meant for a Honda XR600. (Some might recall, I have an actual XT600 version as well, but that's the smaller diameter version, which is loud as all hell.) It turned out that only the last bit of the snout of had to be slightly remade.
Actually fits nicer than the stock exhaust.
After playing around with various carb jettings and basically only deteriorating performance, I concluded that the only valid resolution would be to alter the cam-timing.
There's that trick from long-time XT owners that if the camchain is stretched just enough, one can breath some new life into the engine, by advancing the camshaft one tooth to compensate for the elongated camchain.
Didn't work, but when I was in there to correct my mistake, I took the time and welded on a bung for my AFR-meter.
Which was the moment, when things changed from a bit strange to VERY INTERESTING.
With the engine off I let the probe (auto-)calibrate for a good 30 seconds.
Kicked the old girl into life and started to doubt the reading on the instrument. 10.8:1 is quite rich and a good explanation for just how well it starts in the morning. But at mid RPMs it would completely stop working and break up. Now as you can see above the airfilter cover looks like a sieve and the jetting at this point was close to stock, yet the bike was running so rich it was unbelievable.
So surely it must an ignition issue. Found a new coil, swapped it in. Same result.
So attempt to reduce the amount of air with some lovingly applied masking tape. Same result.
Float levels - a classic. Ruined fuel economy, made starting annoyingly difficult. Same result.
At some point I got very annoyed and got my hands on these puppies. (Haven't tried them out yet, but I will!)
Then even threw in a spare TM33 carb body, which would have been a lovely solution to a problem, I didn't have, but the carb body is too wide to make it work.
With the carbs basically ruled out, engine timing ruled out there's one thing left and that's ignition timing. Now the ignition is non adjustable on these beasts. With the engine on TDC, there's this lovely little mark showing up EXACTLY on the pointer. It does look kind of odd for a TDC-marker though.
Well, it looks odd, because it isn't a TDC-marker and strangely enough, the engine will run, if timed to this one. I still haven't managed to measure just how many degrees out this actually was, but I'd say at least 15 degrees early.
At which point it was just a matter of taking everything apart again, rejet to the last known working jetting and then do 500km of this. The Dre-XT-Stück is not meant to become some mad super sporty offroad racing bike, more of a hiking boot with a nice backpack that I can tour on for hours and just chill. The fact that she's got some get up 'n' go coming from that 633cc engine won't exactly do harm.
In an attempt to express my gratitude to the old girl, I got her some jewelry. New shiny bolts for the yokes to be precise and even more importantly flushed the clutch cable with oil. Lots of oil.
In return those panniers proved to be incredibly for all those transport-duties that would otherwise be completely impossible to achieve - like delivering "Strudel" from my Grandma to my girlfriend.
No comments:
Post a Comment