power loss

So I've been working on a project for about half a year now. I got the bike running a few months ago, just needed to rebuild the carb. I rebuilt the carb, and tried to start the motorcycle. The motorcycle tried to start but didn't. I added some gas, same thing again. It didn't start. Now there's...

So my 81 400 special will run and take off like a rocket in town but on the highway in 5-6th gear around 4500-5k rpm it boggs down and I have to drop down to 4th and get back up to 50mph and ride it out. I feel as if it's either not getting enough air or not enough fuel. If I hold the throttle...