Hesitation problems 2003 yamaha wr 450 f

There are two needle screws that can be adjusted to make the engine run properly. Be certain that the carburetor is clean and the diaphragm is in good condition, and the fuel is new. The two needle screws mentioned above should initially be adjusted at one turn open from turned in all the way (lightly seated). Each of these needle screws performs different functions. One is for idle and throttle response (this screw is marked "L" and the other screw is marked "H". L and H are marked on the carburetor body and also on the plastic "shroud" near the adjustment screws. These screws are not interchangeable, being foolproof since the thread sizes are not the same. When properly adjusted the low speed screw (L) allows the engine to idle properly and throttle response will work properly. When the high speed screw is adjusted properly the engine will have correct power at full speed. Adjust the low speed screw so that the engine idles and when you squeeze throttle all the way to wide open the engine should not hesitate and should come up to full speed and when you drop the throttle it should idle nicely without stalling. Now adjust the high speed screw. Hold throttle wide open, holding it there while you adjust the high speed screw. If this scares you (be carefully so that the spinning chain does not cut you!) you may adjust the high speed screw at idle, turning it just slightly in or out. The high speed screw should be adjusted so that the engine does not run clean at wide open throttle but sputters slightly, slightly adjusted open from running clean to slightly sputtering. When under load (cutting a log) the engine should run clean. Good luck!

these symptoms usually point toward lean on fuel for some reason
most common would be dirty or gummed pilot circuit and pilot jet I would remove carb and take out the pilot jet clean or replace with new - blow compressed air through the hole the pilot jet came out before reinstall
depending what altitude you are a bigger size pilot jet may assist this issue also but clean and replace original pilot jet and circuit first to confirm

The cylinder is in the front of the bike and on a down hill the oil in the crank case could be pushing past the ring. Yes, it could be an over full situation. Only run the recomended amount of oil. You can actually rob yourself of power and do damage by over filling. I've already seen a guy blow the soft plugs right out of his Yamaha by over filling the oil. Also, be careful when changing your air filter. It can be very easy to drop dirt inside and that will definately score your cylinder walls and cause permanent smoke. It is most likely exactly what you think it is. Good Luck.

soounds like a leaky exhaust valve to me,,,do a compreshion test first to check it could need the carbs reset up if its running week on one pot this could do it too

If it is old enough to have points then I would check them and make shure they are clean and gapped at .020. if that is noth the problem then it sounds like a fuel issue. Either a weak pump or a dirty carb.

does it have diaphram in carb if so check for slack

Check the throttle cable to see if it is sticking.