old scrambler and paulages might be your best bets on here for help. They know those bikes inside and out. I know paul is pretty busy these days, but a PM couldn't hurt. We have 2 of them (a'69 and a '73) and are still figuring stuff out so, we can't help much with specifics on exactly how to do something.
I would start by cleaning carbs and making sure you bench synch them at least. If you think they are clean enough, clean them again. And then clean them again.
Check your air filters. Check your throttle cables, maybe one or both need some love. They both need to pull exactly at the same time or you'll have problems. set everything else and do the throttle cables last. check your fuel lines and make sure you are getting fuel at an even pace.
check your clutch cable and adjust it. you can get a free pdf of the manual online.
It's pretty easy to adjust.