When I start my 2004 Yamaha TTR 225 on full choke and pull back on the throttle the bike starts to die. If I let off the throttle it will sound normal again. I have cleaned the air filter and I have cleaned the bottom of the fuel tank. I have no idea what is wrong with it.

Remove the fuel tank , side covers , and seat. Take your carburetor off , clean and inspect it. Check the carburetor top diaphragm. Make sure all the jets are in place and the passageways through the body are clear as well as the jets are clear. Squirt carburetor cleaning fluid through them. Most of all inspect the intake boot for rips tears and separation. Make sure your mixture screw is set to 2 full turns. Reassemble and your problem should be solved.