Honda Rebel 250 Running Rough

Cousin Gonflable here. We are both senior citizens and newbies. My wife bought a 2003 Rebel 250 with 8800 miles on it.

It is running rough, no smooth acceleration and the faster you go the more apparent it is running rough and seems to lack sufficient power. I suspect carb issues.

It starts easily and the choke works fine. I pulled both plugs and they were both black with soot. I cleaned the plugs and put the back in. A new air filter has been ordered, the old one is dirty, I have brushed off the dirt and cleaned out the air filter chamber.

I am hoping this can all be resolved with a carb cleaner fuel additive. Any recommendations on a good additive and how much to mix in? Any other suggestions?

Thank you so much for any suggestions and help.

Cousin Gonflable