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Oil in the Air Box?

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I have a '04 CRF250R with a one week old top end and new Hot Cam, when riding I noticed oil dripping from the drain on the bottom of the air box. My oil is only 3/4 up on the gauge stick so the oil is not over filled, and this problem did exist prior to the new top end. Any suggestion on what the problem might be?

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If your bike fell over or you crashed some oil may have run out the engine via the breather pipe form the top of the cam cover into the airbox.

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The catch tube is empty, this is a regular occurance and I do not think I could narrow it down to a crash ( I mean none of us ever crash, Right?) I will pay attention to whether the bike goes down or not.

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More times than not, that kind of oil shows up after a right crank seal failure. Very common for these bikes. I know the '06 seal will fit the '05, but I don't know about the '04. The '06 seal is a better design.

The one thing that does not make sense though is no oil in the pink tube, yet you have oil in the air box. Usually the pink tube will fill first and then it will blow into the air box because it has nowhere else to go.

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I dunno,

My bike flipped over this weekend, and it was running while it was upside down. I got it upright and it started right away. I noticed later that the airbox drain hole was leaking Engine oil, not filter oil. It fell onto the swingarm. I checked the engine oil, it was clean and a bit lower. I took the air filter out and the boot had engine oil in the bottom of it and the bottom of the air filter was wet with engine oil. I changed the air filter and away I went. I don't think my bike is buggered, but who knows. My valves are spec. I think this happens when you flip it completely upside down while it is still running.

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That's why you have to plug the airbox and ditch the tube. Make it a straight shot from the valve cover.

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That's why you have to plug the airbox and ditch the tube. Make it a straight shot from the valve cover.

Could you explain this further?? I have heard about changing this set up but cant find any detailed instructions...

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Take your gas tank off the bike and disconnect the tube on the valve cover and disconnect the other tube from your airbox. Take some new tubing of the same diameter and run one single tube from the valve cover down with your other tubes. Make sure you re use the clamp so that it disconnects from the cover easily. Make sure you are careful and route it away from your exhaust mid pipe. Plug your airbox where the tube connected. I used the plug at the end of the pink tube and thickened it up a bit with a piece of tubing and one of the circle clamps for a nice neat look. Then remove the holder for the tube (by the counter sprocket) to clean it up around there.

Swapping main jets takes about 1 minute with everything out of the way.

Now your airbox will never fill with oil...... but you should still not pollute. Rebuild the top end dry so that barely any oil will ever leave your valve cover.

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Hey the same thing happend to me, except I noticed the oil on my air filter. Had to get a valve seat re-cut, you might want to check that out.

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Take your gas tank off the bike and disconnect the tube on the valve cover and disconnect the other tube from your airbox. Take some new tubing of the same diameter and run one single tube from the valve cover down with your other tubes. Make sure you re use the clamp so that it disconnects from the cover easily. Make sure you are careful and route it away from your exhaust mid pipe. Plug your airbox where the tube connected. I used the plug at the end of the pink tube and thickened it up a bit with a piece of tubing and one of the circle clamps for a nice neat look. Then remove the holder for the tube (by the counter sprocket) to clean it up around there.

Swapping main jets takes about 1 minute with everything out of the way.

Now your airbox will never fill with oil...... but you should still not pollute. Rebuild the top end dry so that barely any oil will ever leave your valve cover.

Thanks a lot for the info! But one more question, so that hose is used for an overflow out of the valve cover or is it an air breather line also? Reason being why did they route it to the airbox in the first place? I know it is before the filter but should I still put an inline filter on that hose or is it fine the way it is?

So your saying you just route it to drain out of the bottom of the bike correct?

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Thanks a lot for the info! But one more question, so that hose is used for an overflow out of the valve cover or is it an air breather line also? Reason being why did they route it to the airbox in the first place? I know it is before the filter but should I still put an inline filter on that hose or is it fine the way it is?

So your saying you just route it to drain out of the bottom of the bike correct?

i was told never to do that, like you said that hose is also a breather for the crankcase and if u straightline it your just sucking crap into the motor

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The reason they route it into the airbox is to recycle the vapor (emissions) while gravity accumulates the oil. There is no "sucking crap". My interest in it was peaked when I saw it done by a factory mechanic to a friend's bike.

Cleaner setup and no more tip over issues with oil.

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