Griffdog

Member
May 20, 2010
3
0
Hi, I'm new to this forum and I have an issue thats driving me nuts. I purchased a 03 YZ 450f recently that ran perfectly until i noticed that I was losing coolant due to a blown head gasket. Unfortunately, upon putting back together, I didnt time it exactly correct and noticed that after a min or so after starting it, that the pipe was glowing red due to a valve being stuck open. I thought I could have bent a valve so, I replaced the exhaust valves and after reshimming, and proper timing, I still have the same issue..... Am I missing something? I'm not the most mechanically inclined, yet this is my first 4-stroke, so Im still somewhat of a newbie.... Anyone's thoughts would be greatly appreciated.

Thanks!!
Griffdog
 

Griffdog

Member
May 20, 2010
3
0
ok well i was just wondering.... something doesnt seem right because it didnt glow red before i replaced the head gasket and the exhaust valves..... could one of the valves be stuck open still?
 

oldguy

Always Broken
Dec 26, 1999
9,419
0
As Chili said any modern 4 stroke that is not moving will get a bright red header very quickly. Chances are you never really looked at it before this to notice it.
This is not saying it may not have another problem but the glowing header on a sitting bike is not the indicator
 

knight rider

Member
Jul 17, 2010
17
0
i posted the same thing a few days ago and was worried sick up to this morning. i took it to work today and had one of the guys that races look at it and said it was nothing new especially with the titanium pipe. he said i just never noticed it before. good luck if you look more in to it and post up if you find anything out. dont be a dumb ass like me and put to much oil in it to where it blows out the top and scared the crap out of me.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
Any popping or bogging when ridden? If no, then it is normal. If the exhaust valve had a bad seat, it would run like crap, and pop/backfire a lot! Vintage Bob
 

robwbright

Member
Apr 8, 2005
2,283
0
Are you sure it's a stuck valve (if it's anything at all)?

When I first bought it used, my bike would light the TI exhaust cherry red all the way back to the muffler within about 3-4 minutes of idle in 40 degree weather.

There was a tiny piece of sand in the pilot jet.
 

robwbright

Member
Apr 8, 2005
2,283
0
whenfoxforks-ruled said:
Any popping or bogging when ridden? If no, then it is normal. If the exhaust valve had a bad seat, it would run like crap, and pop/backfire a lot! Vintage Bob

My bike ran fine when you were riding it and didn't overheat while riding (unless you were idling really slow).

It wasn't normal - there was dirt in the pilot. It was so hot the motor would likely have seized in 10-15 minutes imo.

Not saying that's his problem, but I got similar answers when I first bought mine - "it's normal to get hot", etc. . . It was NOT normal for it to get that hot that quick. Now that it's right, I can let it idle for 10 minutes or more in 90 degree heat and it nevere gets that hot.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
A plugged pilot would run horrible and pop, to me. Also the mixture screw adjustments would be ineffective. The carb will find a place to draw fuel from, even completely plugged. Flip the choke on, if you are right, it will run better and the red will go away. If it gets brighter, it has a bad valve in the carb and/or head?
 

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