no gas getting through the carb (see bottom page)

No way Mick, that's great advice, I believe I'm beginning to get my head around proper carb physics. Odd though, when I had a #25 pilot in my bike wouldn't start, wouldn't idle, etc, all the problems listed above, and plugs were coming out white and heat-scored, so I threw in a #27.5. Now the plugs come out black. seems like a hell of a lot of difference for one jet size. Now I know what the idle-enrichment screw does, perhaps I'll put in the #25 and pull the screw out a bit.

The two things I still don't understand are the vacuum diaphragm systems, if they're both seated properly and have no holes in the diaphrams they're probably not the problem, eh?

Yeah, I left that clip in, but it certainly caused me some grief. I was out testing around 15 blocks from my house, cranked on the throttle to check the main jet, got about a healthy (read:boggy and silly) block of acceleration when the clip moved and stuck the needle again. so out came the tools and a shady tree became my workshop for about a half hour while I beat the hell out of the clip to make sure it couldn't move. Seems alright now, but imagine how frustrating if you didn't know who the culprit was! Thrumming along --> bike dies!