Re: Success on 7 deg F motorized bicycle work commute!
My plug, as a matter of fact, is a brand new NGK B5HS. (From Sick Bike Parts. I know I could've gotten it locally. But they're good guys who deserve whatever business I can give. Plus they deserve a sneaky mention, or 'plug'. I've always admired the shift kit and the expansion chamber. Also got their gas shut-off valve. Nice stuff.)
The B6HS that came out of it was exactly the color of perfect toast. I 'riched' the mixture one notch just as fall was coming in. So I don't think I have any 'lean' issue.
I could have a compression issue, I suppose. My head gasket is one I made shortly after breaking in the engine. The one that came with it had a terrible flaw and it leaked fuel mixture pretty badly. The one I made is a laughably dog-eared thing cut out of the cheapest sheet 'metal' with snips that were far too large. I didn't really believe it would work. But it's holding fuel/oil just fine. I never used a torque wrench on the studs. Sometime in the summer of 2012 I noticed one stud seemed loose. When I wrenched it, it seemed to be stripped. I haven't re-torqued since.
Recently I checked the carburetor bowl to see if it's full of crud. It was clean.
But pondering things a bit more, compression troubles are sounding kinda plausible.
Maybe I will just put the new engine in and then see if I can rebuild the top end of this one just for the fun of it.