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KX250F and the mysterious micro-dust that eats intake valves!

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From the very beginning the factory has tried to blame intake valve problems (at least partly) on "micro dust." First they recalled bikes for the anti-backfire screen mod to stop the dust from entering around the edge where the screen extended past the gaskets or seal. Then they blamed it on poor owner air filter maintenance. I thought it was all a bunch of bull, that they were just trying to get out of fixing a design flaw on the part of the valves having pre-maturly released the bike for production. Kawasaki replaced the complete head and valves on our 04 bike, then replaced 1 intake again about 1 month later. I switched the bike to leaded race gas in an attempt to have some lubricant and cushioning on the valve surfaces from the lead. The valves have only been re-shimmed once all summer and the change was pretty even on both intakes. However a friends 250F has run the leaded fuel nearly since new and it has went 0 clearance recently. It lasted alot longer than ours did before we had our initial failure. Once again Kawasaki replaced the bad valves and supplied all gaskets. The local Kawasaki mechanic said it looked to him like the valves had been sandblasted. There were no traces of dirt in the intake from the filter to the carb inlet. However, pulling the top plate off the carb was a different story! This plate had never been removed since the bike was new. It looked like the Sahara Dessert in there with so much dirt. I took ours off and it was the same. Filthy. How? Best I can tell from around the throttle shaft. According to the maintenance manual there is a plastic washer and a steel washer between the pulley part of the shaft and the carb. That's all. The plastic cover that is over the cable box certainly doesn't seal out the dust. And neither does those 2 washers. You might want to check yours if you ride in the dust any at all. Our dealer has a call in to Kaw about what we have found. In the interim I packed the whole cover full of high temp grease till it squished out when the cover was installed to try to stop the dust. Even a Briggs and Stratton lawnmower has a felt washer sealing the throttle shaft. :naughty:Pull the top cover and post results please. If you only ride a watered and groomed track you may not find anything.

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You may be on to somethng. I have ridden nine enduros and five hare scrambles and my intakes tightened up at about 200 miles and have not required any further attention. Only two of the races were dusty though. I removed the screen and used high temp silicon to seal it. It looks like crap inside where it sqwished out (just like the Pro Circuit bikes I saw on a how to segment of Two Wheel Tuesday). I run the fire proof Twin Air and clean it after each ride, use Spectro filter oil and grease the contact point where the filter meets the air box with water proof grease. I have not had the carb top off but will remove it this weekend and seal it up just to be safe. Thanks for the info.

So far, so good and my ICO has 846 miles on it and I only use it for enduros.

A dealer friend said Kawasaki should buy my bike back for research purposes. Evidently, all of the bikes he has sold have had valve problems. I may just be lucky?????

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There are 3 of us with CRF's that ride in dusty conditions.

We all have seen the same grunge inside the carb more so around the slide and card top.

I sealed the carb top, filed down the locating bosses and still I see the same grunge loading up in the carb top.

I doubble checked the entire intake tract and I am pretty sure the dirt is flowing past the air filter.

If you take a white cloth and swab the intake boot you will notice it change color, it looks clean to the eye but there is some residue.

I get it worse then the others because I did the air box and side cover mods.

I clean the filter after every ride, carb once a month, I use filter skins in extreamly dusty conditions and use a libral amount of FFT filter oil.

You can limit the amout of crud flowing past the filter but you can't eliminate it.

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since all of you rm-z/kxf and crf riders are new to the party, consider this:

where do the carb vent lines hang?

and where to they lead to?

where does your hot start open to as well?

:cry: :cry: :cry:

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Bingo, give that man a cigar, got nothing to do with new though, most all vent tubes are routed to the slide area, with the exception of your breather and overflow tubes.

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Bingo, give that man a cigar, got nothing to do with new though, most all vent tubes are routed to the slide area, with the exception of your breather and overflow tubes.

This is all very interesting info, and possibly significant in the search for why some have problems. My KXF was great after a year....I don't ride on dusty tracks. Usually muddy and the carb was also clean, even the slide area.

Also related is someone's observation that road bikes rev just as high as these mx bikes and don't have the same problems. Not much dust on the roads I drive on.

So, assuming that this is a weakness, what can we do about it pro-actively to stop the dust issue....just put foam on each tube, something more formal and effective?

Keep the great info coming....

Mark

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Linco,

That thing looks just about right. What did you buy for $3 at a hardware store that does the same thing? I like $3 more than $34.95 :cry:

And another question as I'm not a carbie expert... are all the carb hoses for overflow, or do some provide a vent to allow the carb to work properly? If so, is it safe to run them all into a catch can and not mess up jet settings, etc???

mg

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Those are interesting items. Carb lines druel gas, so if you route your vent lines up and plug them into that can, the vent line will plug. I guess you will have to mount that can below the carb some place.

What do you think is in the can, nothing? Is the theory that you just convert 5 potential dirt entry points into 1? I think you still need a vent line routed from the can upwards, so fluid doesn't block the drain line by drawing a vacuum. Although the volume of the can will help prevent that.

I suspect not much crud works its way up a skinny carb vent line, but maybe since most carbs also have a tee fitting in the lines and route one hose up, to prevent the vacuum thing, maybe that is the line that lets in crud. I guess you wouldn't need a tee fitting for each line with this can, its a bit simpler in that respect. Seems like it might be neat to have a fliter screen on the open ports.

I thought the original theory was that the wheel on the carb for the throttle cables was not sealed well, the carb manufacturer needs to do some work. If people see large amounts of dust from this, then that seems more likely then vent tubes. Although a vent tube can is kinda neat. If I had my welder, I could make one.

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Isnt this the "same" carb thats on the yzf? how come its not having said problem? Though I do see the point that your all discussing I just dont see how a blue bike can not have the same problem. Also remember recall for the hot start..... could that be wear the dirt comes from? I mean all they did was a zip tie, yamaha doesnt use a ziptie and they have no problems. anyhow just a lil more input for the thoughts of others.... I have been down since march with my kxf and want to know why the valves are doin such before I put it together. :cry:

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Hey Mark,

Here is what I did, I went to a hardware store and got a paint sample can. I drilled the 5 holes plus the sixth for the crack case and an extra hole for a vent. You would be suprise how much fuel you can see in there. Especially if you crash. :cry:

crf%20apart%20003.jpg

I have it zip tied to the breather that used to be in the air box. I bought the applied relocator breather. The can sits at an angle. :cry:

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hey linco ...do you have any holes that let that can breath ..i think i am going to do this since i have yet to have any problems with 20hrs on the bike ...and what kind of silicone are you guys using for the top of the carb

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Isnt this the "same" carb thats on the yzf? how come its not having said problem? Though I do see the point that your all discussing I just dont see how a blue bike can not have the same problem. Also remember recall for the hot start..... could that be wear the dirt comes from? I mean all they did was a zip tie, yamaha doesnt use a ziptie and they have no problems. anyhow just a lil more input for the thoughts of others.... I have been down since march with my kxf and want to know why the valves are doin such before I put it together. :cry:

Right wills, you have a point there. Nonsense all about the microdust. Not to mention the debate about filteroiltype, oilbased vs. waterbased. CRF's raced on icetracks have valve problems, and certainly no dust there. I bet on:

1. poor springs

2. hi revs

3. poor valve material/coating

4. size and weight of intake valve (Yami-3 valves!)

5. bad valve alignment to seat

5. fuel (may be even more critical than suspected)

Note that I do not even list frequent oil/filtercanges to valveproblems. Not changing the oil causes premature wear of other things, but is not the #1 factor to valveproblems.

But what would I know. :cry:

What would be the next great finding causing the issue - too much, say.. nitrogen in the air?? :cry::lol:

Fact is these are hi-tech racing bikes, some better and some worse designed with individual differences, man made. :cry: :cry:

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I couldn't agree more SureBlue. Mirco dust....come on now!

Lets not forget poor coolant flow resulting in uneven temps across the head.

carbon build up on the valves and .......... jetting. Run it lean and it will run hotter.

Joe

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The subject at hand for those who have trouble figuring it out is serious amounts of dirt getting into the slide area of the carb, and how to prevent it. Thanks to those who posted relevent information. :cry: All that other stuff has had plenty of attention already (hot spots, overheating, coolant flow, overrevving, etc). Feel free to continue to rant and rave on those issues in the other threads that exist. As for the blue bikes not having trouble, may I remind you a YZ250F has 3 intakes so they may be of different weights, less radical cam profile etc, so really not relevant to the KX250F in a lot of respects. Whether the dirt is actually causing the valves to fail or not it isn't good for the rest of the motor and is especially dangerous when it causes the throttle to hang as has happened to a local rider.

As for the vent tubes a thought comes to mind of using the small fuel filters used in the fuel tanks on chainsaws and weedeaters as a simple and lightweight way to stop dust and still allow fuel to drain thru. They simply plug into the hose. Keep the ideas coming and maybe we can fix these great running bikes without going bankrupt in the process.

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have you ever thought maybe dirt gets in through the recall for the hot start plunger? I mean that ziptie could have squeezed it up enough to let dirt in there.... also instead of fuel filters... why not use some vent line blocks.. all they are is 1 way valves. and they are small, lightweight and not cumbersome. anyhow has someone gone with aftermarket companies and seen the "microdust" problem happen with a motor rebuild? I mean if it happens with the carb wouldnt someone with an aftermarket motor rebuild have this problem? Not to burst your bubbles but if this is the problem I can solve the problem with my bike, but I dont think thats it.

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Fellas, the manufacturers know exactly what causes the problems, but they won't tell. We only get bad excuses and explanations. Someone should squeeze their balls til they turn purple... microdust my :cry:

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what would that give them? if they know what is going on and not telling us they're only hurting their reputation. it doesn't make any sense at all.

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As for the vent tubes a thought comes to mind of using the small fuel filters used in the fuel tanks on chainsaws and weedeaters as a simple and lightweight way to stop dust and still allow fuel to drain thru. They simply plug into the hose. Keep the ideas coming and maybe we can fix these great running bikes without going bankrupt in the process.

I was thinking along those lines, and figure it would be a cheap experiment to see if they do indeed catch much dirt. Figure I'd put them fairly high up above the swingarm so they aren't swinging around and see what happens. While my tracks really aren't dusty, still feel it's a weakness worth addressing.

Mark

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