Exhaust gets read hot on my 2004 yz250f - 2004 Yamaha YZ 250 F

the valves my friends does the same thing

ONLY if you painted it with bright red exhaust heat paint.. get it serviced before you damage your bike,.

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

no buddy your mixture is too rich which means to much fuel is going in and not enough being burnt so the access fuel goes in the exhaust and then gets burnt in the exhaust which is a explosion so you get a back fire to cure this problem you need to screw the mixture screw in which is located on the carb a picture below will demonstrate turn this screw 1/4 of a turns in this will decrease the amount of fuel going in and stop backfiring good luck bud

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