2005 Yamaha yfz450 acts as if out of fuel.

[Brad Leeson]

What's going on party people? First, thank you for allowing me the opportunity to be here. I recently purchased a 2005 yrs 450 and have yet to run the bike at full throttle. The bike fires up, idles, seems like everything runs fine except a little popping when you let off the throttle or until you hit 5th gear. It runs strong; no bogging or sluggishness until you hit 4th gear and open it up. Then it begins to act like it's out of gas or the about to be out. I can pull over and sit for 5-10 min and it runs strong again until you open the throttle. I have the carb off the bike to clean and wrote down a list of factory and what I found installed. I also listed other key factors and hope someone can help and explain. I'm new to the scene and have no prior mechanical experience but my theory is worst case scenario I have to take it to the shop anyway so why not learn. I actually enjoy it. Lol. Thanks a million. Hope to get back on the trails soon. 

[quadmaniac]

Nice write up, very detailed. I would probably check with the manufacturer of the exhaust what recommending jet sizes to use. My first guess its not jetted properly. Normally with aftermarket exhausts, they ask you to re-jet the carb. It may need to be adjusted as well.