My header pipe on my 2003 yz250f gets cherry red hot when i start it up real quick do i need to change air filter, spark plug, valve adjustment, or get the carb rejetted thanks

It sounds like the carb just needs to be adjusted. If the mixture screw (air/fuel) is too far in, it will cause it to run lean/hot. The high idle is also just an adjustment often cured when you get the air/fuel mixture set correctly. Back the mixture screw out in 1/4 turn increments (turn left) until it bogs a bit. Then turn SLOWLY to the right until it just starts to smooth out. Run it a bit there and see if it helps cool the head pipe down & lowers the idle. It really sounds like you currently have a lean condition.

check ignition timing as red exhaust indicates timing too far retarded

I would check sthe spark plug gap. Set it to 0.9mm
If too close it won't ignite properly also is the exhaust pipe standard? If not the timing and mixture will need adjusting.
Hope that helps.

That sounds like it is running too lean. You may need some carb adjustments to account for your altitude.

Any reason you had to change the jetting??New pipe,Intakes.?But,even though you may have it a bit rich on idle the pipes WILL get very hot,very quickly without some sort of air flow over the front of the motor and radiator.At the very least,have a strong fan blowing directly on the front of the motor if you are going to let the bike run and you are not riding it.I have seen the white plastics in front of the radiator distort from the radiant heat.Don't idle them for in more then 20 seconds.It can do heaps of damage.Ride the bike and see if its running well.When you stop,turn it off.All the yz and wrf will get very hot at idle.Hope this helps

Check the valve clearances and timing and for any air leaks around the intake manifold....Good luck matt .

your either too lean on your fuel air mix screw or your jetting is off