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Airbox YZ250x

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Let's talk about the airbox on a YZ250x.

Can someone explain what the purpose is, of the large rectangular opening on the bottom of the airbox ?  I assume it is to let water out,  but would it not also let water in?!?  What would be the downfall of completely closing it in, and only letting the airbox breathe from under the seat? 

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.....back story is that I got water in my engine, and I can only assume it came through that opening in the airbox.  The water wasn't deep enough to get in anywhere else (maybe).

20170616_064943.jpg

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its just a drain hole - yeah i know its a stupid design - my ktm has a better drainage system - grommet and a drain tube thru the grommet

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It's the exact same airbox as the YZ. Motocross tracks typically don't have 2 foot deep water crossings. It's purpose is to evacuate the airbox as fast as possible if water happened to get "splashed" into the box.

 

 

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It would be nice to plug this hole. I was concerned this weekend with a bit of a water crossing. This bike needs more of an upper snorkel. 

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For all my bikes I have used the blue belray airfilter oil and have submerged my bike multiple times along with my sons yz85 and yes there are droplets on the outside but nothing has ever made it in... Also I grease the lip of the filter. The stuff is pretty sticky and I do think it restricts some airflow but man it traps everything and is waterproof ..

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When I found this I was shocked about how low it was......I have been wondering the same thing. Please let us know how the bike runs if you close it up!

Edited by davevinc1080

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Mainly for water and debis dropout. Sealing it up might take away from it's breathing but I doubt it would be enough to change characteristics and/or jetting. 

Bottom line (or airbox), if you do a bunch of water crossing in the depths to the middle of it, seal it up and run it. Many 4 stroke or other brand 2 strokes are very restrictivly closed up. 

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Sealed it is.  

I'm obviously gonna see if closing it off restricts breathing into the carb.  If it does, I may open up some breathers on the side plates.

Or, I could stay the hell out of sketchy creeks, but what's the fun in that? 

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9 hours ago, CampX said:

Sealed it is.  

I'm obviously gonna see if closing it off restricts breathing into the carb.  If it does, I may open up some breathers on the side plates.

Or, I could stay the hell out of sketchy creeks, but what's the fun in that? 

Years ago they used to make 1" or 1 1/2" pop in foam filter thingys. It was an aftermarket deal to open up the air box on the sides, you drilled the hole and then poped them in. The foam filter material was removable, cleanable, and re-oilable, was a trick set up for the bikes that needed to be opened up to breath, and you could place them as high as you needed on the air box.

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"Years ago they used to make 1" or 1 1/2" pop in foam filter thingys. It was an aftermarket deal to open up the air box on the sides, you drilled the hole and then poped them in..."

Something like this, right?

t171_1d30a1166159591a95c96ef2b619b53b.jp

http://shop.unifilter.com/p/air-box-filtered-air-vents-6-pack

Back to the YZ airbox, a smart design would be a simple one-way flap on the bottom of the airbox that would remain closed until pressure from inside the airbox (presumably water) would force the flap open, allowing the water to drain out.

It's a million dollar idea. Somebody get on it.

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6 minutes ago, CaptDan said:

"Years ago they used to make 1" or 1 1/2" pop in foam filter thingys. It was an aftermarket deal to open up the air box on the sides, you drilled the hole and then poped them in..."

Something like this, right?

t171_1d30a1166159591a95c96ef2b619b53b.jp

http://shop.unifilter.com/p/air-box-filtered-air-vents-6-pack

Back to the YZ airbox, a smart design would be a simple one-way flap on the bottom of the airbox that would remain closed until pressure from inside the airbox (presumably water) would force the flap open, allowing the water to drain out.

It's a million dollar idea. Somebody get on it.

That be them. UNI, should have figured. Sister worked there years ago and I still have a connection with Thomas... 

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6 hours ago, CaptDan said:

Back to the YZ airbox, a smart design would be a simple one-way flap on the bottom of the airbox that would remain closed until pressure from inside the airbox (presumably water) would force the flap open, allowing the water to drain out.

It's a million dollar idea. Somebody get on it.

What if there was a malfunction and the flap didnt open ?  :banghead:

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Well, then it would be no different than if the bottom was sealed, like the O.P. did.

And the simpler the design, the less the chance of something going wrong, or so they say! :devil:

 

 

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Seems that the air boxes on the bikes I grew up on (IT's KDX's etc...) were sealed except for a 1/2" or 3/4" rubber nipple hanging off the bottom. It was very soft rubber and had a X shaped slit in it. Water passed right through when you rode wet stuff. If you rode dry stuff, it would sometimes collect debris. All you had to do then was pull the spring clamp off and clean it. This technology has obviously been superseded . :thumbsdn:

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