My Yamaha seems to run fine with the choke mostly open, as I try to close down choke it starts to pop and exhaust pipe gets red. I think I may need to adjust rich/lean mix. Where is this adjustment on my carb and which way will I need to turn it? Any help would be appreciated...

 

The air/fuel mixture screw is probably what you are asking about, but that won't cure your problem. The mixture screw only controls the idle and off idle circuit of the carb. It sounds to me like you're having a problem with the main jet, which is inside the carb. If it was running well before and then started giving you trouble, it's probably trash in the carb that is blocking the passage of fuel resulting in a lean condition. Without being able to listen to it myself, my best guess would be that you need to pull the carb and give it a good cleaning.