If the carb has been drained of bad gas and the spark plugs have been replaced and we know the bike has good compression. Maybe the jets are clogged? it's either fuel delivery or ignition related issue. It's probably bad gas left in the tank and needs to be drained.
I ran into some bad gas from Chevron before and it caused my bike to be sluggish and eventually stall. I checked my fuel delivery and ignition, found out it was good, my last resort was to drain the fuel in the tank and poof! everything went back to normal.
1. SLK 230K AMG SPORT
2. VW RABBIT 2.5
3. 08 Ninja 250R Track Prepared