i have a problem. i just traded my race ready 300ex and now a proud owner of a 400ex with a 416 big bore kit. iI rode it for the first time yesterday and i started it and let it run for a little bit. i looked down and the header pipe ( the part that goes in to the motor) was glowing red. Any body that has any comments please let me know. please help

 

Sounds like the bike is running lean and might be in need of a jet kit to compensate for the bore kit,if it already has a jet kit you may need to richen up the mixture screw by turning it out more & check the air filter to make sure it is not clogged up but the issue you have is pretty common.Usually with any mods including removing the stock airbox,big bore kits,cams and exhaust proper jetting is required if not you run into heat issues caused by leaning out and it's not good on the engine.Your spark plug reading is the key to the engines running condition,that's where I usually start