Thing is, I'm not sure how it could be a blockage or similiar since the bike idles and pulls right at all other times. It only lasts maybe 20 seconds or so after I take it off the stand too, which would make me suggest float levels or something, as if it were going out of whack while on its side but adjusting, then having to readjust while stood up. But if it were that, it should go wrong on long corners.
Stumped
But never mind, I fixed the clutch (well, put off having to strip it anyway) and the rear brake light today so the list's getting shorter. It's going in for rejetting as soon as I get my act together and all the little things fixed so the mechanics don't take the mick, that might sort it out.