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A little history about my problem. I've ridden my 2nd hybrid three times this year. On this bike I installed an Airstriker carb. It came off a running bike and was very clean, but I took it apart and cleaned everything just to be sure.

The last two times I've gone riding, it has been very, very dusty. After the 1st ride in the dust, I cleaned the air filter and greased the rim before installing.

During lunch on my 2nd dusty ride, I went to swap main jets and found a lot of dirt in the bottom of the float bowl cap. My only thought at the time is that I didn't get the air filter seated properly. I checked it and didn't see anything obvious.

Once I got the bike home and cleaned it up, I removed the air box from the bike and was expecting to find a lot of dirt/dust inside the air boot. To my surprise it was clean.

Spending some time doing Google searches led me to some posts of CR 250 owners complaining of something similar. They tracked the problem down to dirt being sucked in through the vent hoses.

Sure enough, that is how dirt got into my carb and engine.




The vent hose that attaches closest to the choke had the most dirt.


I popped it off and stuck a q-tip in there and got this.


Then I stuck the little red straw from the carb cleaner can into that vent and let everything run out into a clean container. This is what came out of that single hose.


So it looks like I'll be buying the little filters that they installed inline on the vent hoses to keep dirt from entering the carb.

Has anyone with an Airstriker carb experienced this? I've never had this problem with any of my other bikes or my other hybrid that used the OEM carb.

I have had mine for about 3 years or so and never had that problem.

On the CRF250X I used to own, I ran my vent lines into a small automobile smog filter that I had located in the air box. This precaution was due to factory race teams determining that premature intake valve wear on those bikes was at least partly due to dust getting into the carb throat by way of the carb vents.
Not an expensive fix, and there are lots of little smog filter shapes to choose from.

I wonder if something else is behind the problem here tho' like a worn reed valve? Just fish'n.....

kawagumby wrote:On the CRF250X I used to own, I ran my vent lines into a small automobile smog filter that I had located in the air box. This precaution was due to factory race teams determining that premature intake valve wear on those bikes was at least partly due to dust getting into the carb throat by way of the carb vents.
Not an expensive fix, and there are lots of little smog filter shapes to choose from.

I wonder if something else is behind the problem here tho' like a worn reed valve? Just fish'n.....

The threads I found were for the CRF250's. I don't recall seeing an explanation for why the dirt was being sucked in. The focus of the threads was on filtering the dirt out.

My reed valve isn't that old and all the reeds are laying flat and none are frayed. Now I'm curious about what you said, how would worn reeds cause the carb to suck air through a vent tube?

Just speculation on my part, wondering if worn reeds might cause higher than normal intake tract pressure fluctuation that might impact connected carb chambers that have vents to the exterior - there has to be enough sustained negative pressure in the vented areas to draw in the dirt as you have pictured. The only time I've seen that much dirt drawn into a carb (other than intake tract boot leaks or air filter problems) is when the carb slide cap doesn't seal correctly, which includes the cable fitting.