04 yz450f red header, popping on decel

2 replies to this topic
  • 03_yz_250f

Posted April 23, 2013 - 11:22 AM


just picked up a 04 450 and the header pipe turns red only a couple minutes after starting and idleing, it also pops alot on decel, the bike starts fine and i read from alot of people this is normal but my buddy has a 08 rmz 450 that doesn't pop at all on decel, i have turned my fuel screw out a turn and has made it pop more if anything, anyone know the stock amount of turns out on the fuel screw?

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  • grayracer513

Posted April 23, 2013 - 12:02 PM


To begin, different engines have different personalities, and it's just a part of a healthy YZ450's nature to pop off "some" on deceleration, even though other properly adjusted engines don't. Chevy small blocks do it, big Mopar hemi's not so much. Same thing.

Secondly, realize that there are several causes of abnormal decel popping. The two most common are lean idle mixture and an air leak in the exhaust. When troubleshooting and/or correcting this, you should always start by verifying the exhaust system first. If you fatten up the idle to get rid of a pop caused by a leaking exhaust system, you'll have an engine that runs rich, stalls on sudden throttle closings, and probably still pops. The most common points where leaks occur are the mid pipe joint, the head joint, and the joint of the mid pipe to the muffler, if one exists.

Once you're sure the exhaust isn't the culprit, start with the engine warmed up completely and idling. Turn the fuel screw in until it begins to slow or turn rough. Then back out just until it smooths out. That should be at around 1.25 and 2.5 turns out from seated. If you end up at less than 1, you need a smaller pilot. If more than 2.5, or the whole exercise seems to not do anything, the pilot is either too small or is partially or completely clogged.

The glowing header, again, is normal to a degree. It's normal to see the header glow dull red to red after a minute or so of idling when you are in deep shade or twilight, but not bright red or orange out in the light. Both the above causes apply to an excessive glow here, too.

  • 03_yz_250f

Posted April 23, 2013 - 12:24 PM


Thanks for the info! I have checked the exhaust and it was leaking just a bit at the header to slip on clamp, I only notice the header glowing in the garage, if I am out riding in the day I cant see it glowing so I guess everything is normal witch is great.

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