The 650 as stated before doesn't have CDI, it only has a very basic electronic ignition, think of it as an electronic set of points. It will either work or not. The easiest thing to check first is your advance unit, hook a strobe type timing light up to the bike and and make sure your ignition is reaching full advance, off the top of my head I think this occurs by around 2500rpm. But if I had to guess at the most likely cause, I would say the shop has stuffed up majorly on the carb clean and the carb slides aren't opening properly. The 81 650 is fitted with CV carbs and the slides aren't connected to the throttle like the earlier PD type carbs, they are opened by vacuum. The throttle only opens a butterfly between the slides and the engine. Now, if they somehow managed to screw things up so bad that these slides aren't opening then the bike effectively has a smaller carb on it, this will make it pull like a tractor low down in the rev range but it will be strangled at higher revs. If the shop can't handle a simple carb overhaul I would not take my bike there.
