airboot/intake whistle

I am hoping to hear from you experienced YZ-450 owners on something I noticed about my ride during breakin yesterday. I bought a left over 04 Yz-450 in January and have been staring at the thing for months in my shed. Well, I finally got to ride the thing yesterday to break it in, and noticed a whistle that I couldn't locate. It got louder the more I gave it throttle. I called the dealer and they weren't a lot of help other than to check the head gasket and other obvious areas for leakage. They did say to bring it in and they would check it out though.

I took it to the dealer today since I could not find the source of the whistle, and lo and behold, the noise is the sound of the air going through the boot/filter. They spent quite a while trying to figure it out, until they took the seat off and it got louder. We tried putting grease around the filter bolt hole, and this didn't help. All they said was to try another filter. At least it doesn't;t sound like anything mechanical.

I am worried that there may be a leak somewhere that we didn't find, so is there anything else I should look for, and has anyone else had this happen to them?

Dont worry it is just the air going through the air boot.

Should I look for a leak in it or is just the velocity of the air? My buddies crf-450's don't do this, and we all know what a leak can do to the internals....

If it whistles, I would, as you seem to be, be concerned that there is a leak in the boot somewhere. Fortunately, there are only two places where it can leak; the flange at the air box, and the clamp on the carb. But it doesn't make sense that either of these would be louder with the seat off, since neither of them is under the seat. If your airbox is reasonably clean (yeah, right) you could try a quick test on the driveway with no filter. That would narrow it for you. You can do better than the OEM filter, anyway.

It probably isn't anything to be worried about.

find another airfilter to see if it still does it - I have not experienced this on any of my bikes

once my airboot to the carb clamp was overtightened. This caused it to not be completely round therefore not sealing to my liking.....

The filter is a brand new twin air unit just oiled the day before. The interesting thing is that it won't do it at idle or sitting still... you have to be in gear and on the throttle. :naughty:


The keihin also seems to make a whistle, I noticed it when I installed one inplace of the cv mikuni that my ktm 640sm came with, though can't say I noticed it on my YZ maybe I'm to busy just trying to stay upright.

It's normal, many of the 426 guys used to talk about this. I think it's the air going by the slide in the carb. It's not a leak on the head side of the carb or it wouldn't idle or would idle very poorly. It's not a leak on the airbox side of the carb because at just over idle there's not enough vacuum or velocity there to cause a whistle, so it must be coming from somewhere inside the carb in which case I woudn't worry at all. Mine's been doing it for years, seems to come and go with the weather (that or I just don't notice it anymore). Don't sweat it, it's normal. :naughty:

Thanks for the all of the input. Being new to 4 strokes, I'd rather work on learning to ride than worrying about all the things that are different. I am fairly possitive that I'll get over all the 2-stroke habits I've aquired over the years and learn how to put the Yz power to good use. One thing I can say is that it probably isn't a good idea to take your first 4-stroke ride in deep whooped out sand! Can you say STALL, STALL, STALL! :naughty:

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