Yeah don't add anything to gas. This bike is carbureted, not fuel injected. There's only really two reasons why it would act that way. 1) the carb is gummed/clogged up with debris from crappy air filter setup (lol @ duck tape) 2) the fuel/air mixture is off.
I would first check that you have the proper air filter installed and that there are no gaps in the housing, gasket areas. Make sure there are no tears in the paper. Take it off and physically look inside to make sure its not gummed up. If that's all good then empty the tank and put in a gallon of fresh high octane gas. If that doesn't help its time to clean the carb. This is all assuming someone didn't rejet the carb at some point. That's another conversation entirely.
2009 Honda Rebel 250
Custom Bobber "Enforcer"