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Air box mod?

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It's a very common mod and part of the closed course competition mods bulletin published by Honda

Most do something with the exhaust as well.

Note that anytime you change air flow in/ out of motor, you'll need to rejet the carb as well

Jim

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Many 250X owners, including me, have done the airbox / jetting mod.  It's a very easy way to get more power, without much tradeoff.  It should even start easier.

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Many 250X owners, including me, have done the airbox / jetting mod.  It's a very easy way to get more power, without much tradeoff.  It should even start easier.

How dramatic of a difference did it make in power for you?

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Many 250X owners, including me, have done the airbox / jetting mod.  It's a very easy way to get more power, without much tradeoff.  It should even start easier.

How dramatic of a power difference did it make for you?

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I'd say a large majority of the 250x owners on here have it done.  Most find the bike runs smoother overall with a bit more power when combined with rejetting.  The bike comes lean stock, opening the airbox will make in even leaner, so definitely plan to rejet if you do this.  

 

As for the increase in power, couldn't give you an exact number, its pretty subjective but noticeable.

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Just a note; if you like deep water, be careful how much you open. I stuck to the top only as I often have the bikes up to the seat in water

Jim

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Good point Jim.

 

I've had the jets, a putty knife and my heatgun ready to go for a few days now.  After reviewing a lot of threads, I think I'll pull the snorkel only.  Might even cover that with a homemade pantyhose filter.  A lot of folks get good power changes, and retain better gas mileage with the smaller hole/smaller jets approach.  If I don't like it I can always cut more and rejet again.  My valves seem to be fine, but I'm listening to the "less dirt in the airbox is good" theory for my 2007.  

 

Plus... I dropped a KLX in 3-4 feet of water last season and couldn't believe how fast the crankcase filled up with water (airbox cover was totally removed).

 

Sorry for the highjack - if I just remove the snorkel and leave the stock can as is - anybody got a good mainjet number for me?  I've seen anywhere from 135 to 150 mentioned in various threads. I bought 150, 152 and 155 thinking I'd remove the entire top but that may have to wait.  How much would drilling the baffle add to that?

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I have the entire top and part of the rear of the airbox off, I also removed the backfire screen from the filter cage. My filters don't seem to get any dirtier than other people's. I'm also running a ported R head and high compression piston, helps keep me in front and out of the dirty air ;)

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Good point Jim.

 

I've had the jets, a putty knife and my heatgun ready to go for a few days now.  After reviewing a lot of threads, I think I'll pull the snorkel only.  Might even cover that with a homemade pantyhose filter.  A lot of folks get good power changes, and retain better gas mileage with the smaller hole/smaller jets approach.  If I don't like it I can always cut more and rejet again.  My valves seem to be fine, but I'm listening to the "less dirt in the airbox is good" theory for my 2007.  

 

Plus... I dropped a KLX in 3-4 feet of water last season and couldn't believe how fast the crankcase filled up with water (airbox cover was totally removed).

 

Sorry for the highjack - if I just remove the snorkel and leave the stock can as is - anybody got a good mainjet number for me?  I've seen anywhere from 135 to 150 mentioned in various threads. I bought 150, 152 and 155 thinking I'd remove the entire top but that may have to wait.  How much would drilling the baffle add to that?

 

 

 I removed the snorkle on mine, then heated up a 1" pipe and poked 6-8 holes through the top.   I left my backfire screen in and have stock exhaust.

 

 With that (and I ride at sea level),  I have a #42 slow jet, #158 main, and a JD red needle in 5th position.

 

 Think I'm on the rich side, but it runs well.

 

Jim.

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Thanks Jim.  Always better to be a bit on the rich side.

 

I have 6 of those little 1" round airbox filter insert thingys in the garage.  I bought but never used them on my TE610.  They may get their opportunity on the CRF.  Think I'll try the 152 main and move to 155 if I feel like it needs it.

 

They're blue but I don't think the Honda would mind. 

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