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Water And Dirt In Carb - ‘06 CR250

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You need to seal your airbox.  These last gen cr250's (02-07) suck dirt right past the filter.  Pull the airbox, seperate the boot from the box and remove the seal.  Get some 3m gasket sealer from the local auto parts store and put the boot back together to the box with the sealer as the gasket.  clean your airboot and airbox completely (probably before you glue them back together) and then use grease on the sealing surface of your filter as insurance to keep from getting dirt past the filter.  The more expensive way to fix this issue is with an mxbonz airbox kit if you want to spend the money on it.  I bought the mxbonz kit, only because my OCD wouldn't let such an obvious engineering design flaw exist on my bikes.

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Do you have an inline filter in your fuel line? I use one religiously and have never had anything im my carbs like that. The in tank filters often fail, I think something in the ethanol gas eats them up. I use a Visufilter and never ever never use ethanol gas. But the bottom line is that you should sell me that CR and end your frustration. I have been on CR's since '86 and never had a leaky airbox issue.

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Believe me, it's coming from your airbox.  I own an 03 and and 06 cr250 and both had sucked air past the filter when I brought them home from the sellers house.  I cleaned and sealed both airboxes and have not had an issue since. 

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After cleaning and sealing airbox as suggested, I would clean carb TWICE and also check reed valve assembly and clean the heck out of that too. Small particles of dirt may be present.

 

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1 hour ago, Piney Woods said:

Do you have an inline filter in your fuel line? I use one religiously and have never had anything im my carbs like that. The in tank filters often fail, I think something in the ethanol gas eats them up. I use a Visufilter and never ever never use ethanol gas. But the bottom line is that you should sell me that CR and end your frustration. I have been on CR's since '86 and never had a leaky airbox issue.

HA!!!  That was a good one.  Took me over a year to find this bike so nah I'm keeping it.  I don't run a fuel filter but this much dirt and oil did not come from the fuel.  I've got 90 hours on this bike now and this is the first time I've seen even a spec of dirt or moisture in my carb.  Also yesterday was only the second time I rode in the rain.  See pic, definitely coming from the air box.  Thing is I have the 4 stroke version of this same year model and never saw it with that one.  But I wasn't on top of my maintenance with that bike as much as I am with this one.

 

 

 

1 hour ago, frdbtr said:

You need to seal your airbox.  These last gen cr250's (02-07) suck dirt right past the filter.  Pull the airbox, seperate the boot from the box and remove the seal.  Get some 3m gasket sealer from the local auto parts store and put the boot back together to the box with the sealer as the gasket.  clean your airboot and airbox completely (probably before you glue them back together) and then use grease on the sealing surface of your filter as insurance to keep from getting dirt past the filter.  The more expensive way to fix this issue is with an mxbonz airbox kit if you want to spend the money on it.  I bought the mxbonz kit, only because my OCD wouldn't let such an obvious engineering design flaw exist on my bikes.

My air box stays pretty darn clean.  I haven't taken it apart and inspected the boot seal yet so that's a possibility.  Crazy though to think the water and dirt got sucked right through the double layer Twin Air that's pretty heavy with air filter oil.  And I always thought I have a good seal between filter and box.  I'll have to do some more inspections when I have time.

 

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15 minutes ago, Mike_80 said:

HA!!!  That was a good one.  Took me over a year to find this bike so nah I'm keeping it.  I don't run a fuel filter but this much dirt and oil did not come from the fuel.  I've got 90 hours on this bike now and this is the first time I've seen even a spec of dirt or moisture in my carb.  Also yesterday was only the second time I rode in the rain.  See pic, definitely coming from the air box.  Thing is I have the 4 stroke version of this same year model and never saw it with that one.  But I wasn't on top of my maintenance with that bike as much as I am with this one.

 

 

 

My air box stays pretty darn clean.  I haven't taken it apart and inspected the boot seal yet so that's a possibility.  Crazy though to think the water and dirt got sucked right through the double layer Twin Air that's pretty heavy with air filter oil.  And I always thought I have a good seal between filter and box.  I'll have to do some more inspections when I have time.

 

It's not going through the filter, it is getting past the filter due to leaks in the filter seal and the airbox to airboot seal.  I use the stock filter on my 03 and a twin air filter on my 06 and both are filtering perfect after the airbox mods that I have done.

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13 minutes ago, Mike_80 said:

HA!!!  That was a good one.  Took me over a year to find this bike so nah I'm keeping it.  I don't run a fuel filter but this much dirt and oil did not come from the fuel.  I've got 90 hours on this bike now and this is the first time I've seen even a spec of dirt or moisture in my carb.  Also yesterday was only the second time I rode in the rain.  See pic, definitely coming from the air box.  Thing is I have the 4 stroke version of this same year model and never saw it with that one.  But I wasn't on top of my maintenance with that bike as much as I am with this one.

 

 

 

My air box stays pretty darn clean.  I haven't taken it apart and inspected the boot seal yet so that's a possibility.  Crazy though to think the water and dirt got sucked right through the double layer Twin Air that's pretty heavy with air filter oil.  And I always thought I have a good seal between filter and box.  I'll have to do some more inspections when I have time.

 

I was finding dust in the airboot on my 2007 no matter how good filter was. I put a MX Bonz sealing kit on and no more issues. With the scarcity of cylinders not to mention the hassle of a rebuild I believe it’s a must have for the 02-07’s. 

The OEM parts were flimsy when new and time hasn’t been kind to that thin foam. 

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MX Bonz it is.

I got the carb super clean, and took the opportunity to wash out my air box and boot as well as wipe both out clean.  I was amazed at how much sand got in there.  Tomorrow will be the reed valves and anything else I see.  And I’m about to hit my next crankcase and top end rebuild, after 1 or 2 more rides.

One more picture, this one may help show how the air filter is sealing.

 

D1D6DE0F-05C9-42A5-881C-50089E7A28F9.jpeg

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The MXBonz kit gets rid of the plastic nubs that honda somehow felt were not a problem on the sealing surface where the filter mates to the airbox.  I still recommend getting the 3m sealer and using it to seal the airbox to airboot junction as well.  That is what I did when I installed the mxbonz kit on both my 03 and 06 and I haven't had any dirt past my filter since. 

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3 hours ago, frdbtr said:

The MXBonz kit gets rid of the plastic nubs that honda somehow felt were not a problem on the sealing surface where the filter mates to the airbox.  I still recommend getting the 3m sealer and using it to seal the airbox to airboot junction as well.  That is what I did when I installed the mxbonz kit on both my 03 and 06 and I haven't had any dirt past my filter since. 

 

Awesome, thank you very much.

 

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I have a 2002. I went with a "poor man's" version of the MX Bonz kit. If you look at the OEM parts list for the airbox, you'll see the case plate-#4 in the OEM parts diagram. It holds the boot to the outside of the airbox. I bought one and put it inside the box, after grinding off the nubs. Drilled holes all the way through where the screws went into the airbox to hold the boot/plate on. Stainless screws with nylock nuts. Siliconed each plate to the box (one inside, one outside),and bolted together. Gasket material siliconed to the case plate inside the box, so the filter seals to the box tightly. It worked great-no leaks- and I don't need to grease the filter to get it to seal. Cost me less than $20.

Edited by Imposing Will
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No matter how sealed the setup is, if it isn't designed with splash guards then muddy water gets in and goes right past the air filter.

I had taken off the splash guard on the intake of my KDX200 and enlarged the opening and then dirty water got in and the carb starting sticking. That ruined my chances that day on the motocross track. :-(

I think generally speaking the design of enduro bikes is better than motocross bikes.

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BelRay filter oil will prevent water getting thru a filter. And if that filter is mounted properly no water will get past it.

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I don't see how any oil can prevent water ingestion.

How an oiled filter works against dust is that as the dust is forced to zig-zag thru the filter it will eventually contact it and the oil there will hold it there.

Not so with water, not at all. Water and oil don't attract each other or stick to each other.

The intake needs to be designed so that muddy water splashed up to the airbox intake will either be diverted away or once in the airbox will be guided towards the airbox bottom instead of towards the filter.

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My region averages 60-70 inches of rain a year. I have never once in 45 years had water get past my filter. I will continue to trust BelRay.

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I used regular silicone for now.  It’s not the 3M gasket sealer but it’s what I have at the moment.  I’m sure it’ll at least be better than before.  I’m still amazed THAT much dirt and water got through, that’s pretty disappointing.

6D0D171E-43A9-4E18-B6B4-6EE38AE435FA.jpeg

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13 hours ago, Mike_80 said:

I used regular silicone for now.  It’s not the 3M gasket sealer but it’s what I have at the moment.  I’m sure it’ll at least be better than before.  I’m still amazed THAT much dirt and water got through, that’s pretty disappointing.

6D0D171E-43A9-4E18-B6B4-6EE38AE435FA.jpeg

The 3m is supposed to be resistant to petroleum products and not break down when it comes in contact with them.  Your silicon will do fine until you can get a permanent fix done and is better than nothing.  

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Because of this I'm updating my maintenance program.  Maybe I set it at every 10 hours or so: Remove and separate air box / boot assembly, clean and inspect, remove and reapply sealant as needed

 

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