So I took the new battery to Og's, and for a wonder there was enough of a gap in the rain that the streets were reasonably dry and I was able to ride the motorcycle around his neighborhood a bit.
Problem is, the motorcycle is still exhibiting the same behavior that it has all along: you can start it and ride it around the front yard a bit; but after about five minutes on the street the engine dies and won't run.
This motorcycle has a funky fuel petcock. Okay, most motorcycles which aren't fuel injected have a petcock with three settings: Off, Run, and Reserve. This one, however, has On, Reserve, and Prime.
The fuel petcock closes automatically, and opens only when sufficient engine vacuum is developed to draw back a diaphragm against spring pressure. It doesn't take much--1 PSI will do it--and the entire idea is to make the motorcycle more convenient for the rider. He doesn't have to switch the fuel on and off most of the time. The only time he ever has to muck with the valve is when A) the bike has been sitting for a long time, or B) when it runs out of gas.
So when you're riding around on the street and the thing dies, the only way to get it running again is to switch the petcock to "prime". This is after, by the way, you've been tooling around for a bit with the damn thing in the "on" position.
Og and I spent the better part of an hour--while doing other things--batting around ideas as to WTF is going on with the fricking thing. Sunday I'm going back over there and I'll try riding it around the neighborhood in "prime" and see if it exhibits any of the behavior it does in "run". If it doesn't, it means there is something wrong with the way the petcock is behaving; if it does the same shit, it means the petcock isn't the problem.
Our thinking is that there may have originally been a diaphragm-type check valve in the vacuum port of the thing, which succumed to the vagaries of age (there was goo in there, we found). If so, it would explain a lot; but we ran out of daylight and energy and dry weather to keep fooling with the thing tonight.
...especially maddening when you get to ride the damn thing and then can't ride it home. But, as I pointed out before leaving, he's a robotics engineer and I'm a freakin' avionics technical writer. This is a motorcycle and it ALMOST works right. If we can't get it working...
"...we might as well just blow our heads off and get it over with," he agreed.
But I got to ride it. This bike has more than enough power for me, and it's going to be fun...when it's working right.
Anyway, so then I leave Og's cave just as it begins raining; and as I'm tooling around rural Elsewheresville it begins raining buckets. The wipers are on high speed and the defogger is running full blast and I'm still having trouble seeing through the murk. Argh.
I get home, put some stuff in the garage, take out the trash; deciding I want cinnamon rolls, I start the oven preheating and peel back the paper on the container--
Cinnamon rolls: BLAM!!!
The rolls blew up in my hand like some kind of sinister IEP (Improvised Explosive Pastry). There were no signs of islamic terror on the container, though, and I was unhurt, so I kept on with my task, secure in the knowledge that at least this time the terrorists did not win!
Then I laughed at how silly it all was. I use Crisco butter-flavored spray to grease the pan; to be mean I spritzed the cat with it. Obviously a little butter-flavored oil isn't going to hurt her any more than it would me, and she'll end up just licking it out of her fur. "OMG, I haz a flavor! I iz tasty like butter!" or some such.
* * *
...took a bit of a break to look over the factory service manual for the bike, and what do I find?
I'd like to direct your attention to callout number 5:
There is the check valve, and its design even fits with my expectations of what it would have looked like before dissolving into black tarry goo.
So there does indeed have to be some kind of check valve there, because otherwise vacuum fluctuations cause the petcock valve to flop open and closed. You can hear it; and this is a not-good thing because it starves the motorcycle for gasoline.
I really, really, really hope this is the problem.
Now I'm going to frost my cinnamon rolls and play WoW.