Dan, thanks for explaining the throtlle thing a little more clearly. you obviously need to replace the carb in question.
I feel like I'm beating you up here but I still can't make heads or tails of your description of the clutch / gearbox issues. matter of fact, so much so that I can't figure out how to ask you questions to help me understand, so I apologize if I seem dense here but this is something that should be able to be figured out by solid logic.
I agree with thud300 and I've read posts here of a guy who's return hole in his clutch reservoir was so pluged that when the fluild in the line got hot it expanded enough to disengage the clutch completely. One of the super knowledgable guy's like SISF or MOB (I think it was) said that the splines on the rear wheel can inexplicably disapear and diconnect the engine from the drivetrain (and not make any noise that would indicate it had done it! ) also looking like a clutch problem.
bingo
he mentioned he could shift it, and it won't move in any gear... big clue. locked up tranny won't shift, ever.
I was thinking hjb spline right from thde start, they fail without warning, Id pull that wheel off, wipe all the grease out of the splines on the wheel side, and examine it closely... the drive side (male splines) are hardened, and seldom go bad, but the wheel side ones are soft, and sacraficial... luckily that hub part is removable, and fairly cheap tonreplace....
you may also have a broken star spring in the clutch, which will prevent correct engagement, but check that wheel hub first, before removing the clutch cover. I don't think the smoke thing, related to any of this either. just another spot to examine further.. if you were clamping on the brakes and holding them on while the throttle was open at freeway speed, for a distance, you likely did heat up the clutch tho, and or the rear hub, you didn't clarify enough of what was going on to say...
oh, kinda late noww to mention this, but as you have found, buggering up a bailing wire fix on a carb for anything other than emergency use to get you home to fix it properly, is both dangerous, and foolish.