Valve, dust in carb isssue...A theory

Here theory about carb dust and possible valve failure.This is my opinion and I invite critizim but I will have my force field up.There was an earlier post about dust in the carburater of someones bike and it seems that is common among many or the CRF 250's x and r. This dust is probably at least partialy responsible for premature valve falure and has been cited as micro dust by Honda as the problem with the valves.Please look at the pictures in an earlier post on dust in carb. There are two vent lines coming into the carburator right above the choke knob on the crf 250's. Those lines if you look closely at the carb vent into the chamber above the carb slide. You will see this if you examine the carb completly.These line are directly vented to the atmosphere and are hooked to this chamber. The area above the slide will develop a vaccum when the engine is running so there is a small vacumm being pulled thru these lines at all times when the engine is running. This vacuum pulls micro(very fine) dust into the engine thru these tubes as a result of the vacuum. Remember these lines are not filtered and this is probably an oversite at honda leaving this flaw open. Remember this carb was designed for a street bike originally. Also note the tubes run underneath the bike in a very dusty situation which only a very small vacuum would probably be needed to pull in the dirt especially micro dust which floats easily anyway. The solution I have right now is to filter the air coming into the carb thru the vent hoses by using a filter at the end of the hoses. My carb no longer has dirt in it because of this move...dont know if that will solve the valve problem but couldn't hurt in my opinion.I expect criticism and it is welcome. This is only my opinion on the issue. Sheilds up now!! :cry: :cry:

Sounds reasonable to me. Did putting these filters on change your mixture any? Maybe you should post a few pictures and what parts you added so others can do the same if they so desire.

Hope it works out for you on the valves.



Here a picture of my setup so far. It is very simple but I am sure can be improved on. I took a RC car air filter(cylindrical with hole part way down center).Cut the tubes so the ends matched.Took a piece of safety wire and strung the tubes evenly togeter by piercing the tube with the safety wire then installed this RC car filer by running exess wire thru the foam after it was pulled on. Then tie the two ends together and tuck on top of the skid plate.The better you can filter the better and you must clean the filter ofter. I'm sure there is a better way and it does not change mixture.

Also if Honda has changed the 05 carb in some way to reflect this problem...they know of it and have corrected. Depends on carb design.

Here's an idea.


PC racing makes this vent system for 2-stroke carbs. I'm sure you can easily use this to filter the vent tubes.

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