overheating

Okay son's new bike 2004 yz450f great bike question if exhaust pipe has turned a blue color is that a sign of over heating my younger son has a 2003 yz250f and the pipe is a more amber color older boy is complaining that the pipe feels hot against his leg at the starting line he races mx yes I checked for fuilds and every thing is topped up I know it sounds like a newbie question but I have watched this site for a couple years first time writing in great site just want to be sure I ride a CFR 450 and I have to say impressed with the Yamaha just wondering if maybe the bike is a little lean bike starts good with choke first time but if left for a couple hours it seems to start better with choke on .

Needing the choke when the motor is cold is normal, that's why it's there. 4-stroke headers get very very hot, that's normal too. Make sure it has a good heat shield. If you want to see how hot it gets, start it at night (in the dark) some time and let it idle for a minute.

The stock '04 YZ 450 exhaust is all titanium, tip to tip, except for the muffler can. Titanium turns all kinds of cool colors when heated. The FMF Ti4 on my '03 turns deep blue clear to the muffler after a hot day's ride in big dunes. Normal. Four stroke exhaust temps are much higher than two-sters, and you really can't make a good comparison to another bike, even the same kind, unless the pipes are the same.

Because a four stroke head is so completely filled with valves, there isn't a lot of direct contact between the combustion chamber and the engine coolant. As a result, a lot more heat is still present when the exhaust cycle comes around. They also are not able to idle at a standstill for as long as the oil burners for the same reason.

As long as it's not barfing coolant all the time, it's probably OK.

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