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Oil in my air filter

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Athame57:
Could a badly seated valve be causing my air filter to get oil stained via Blow-by gas circulator that exists on the CB400F ( I gather it was created to deal with US emission laws). There is no pooling of oil in it's housing and the drain system below it isn't blocked but they are both messy as usual. I have just fitted a new air filter last week but whatever the problem it has made short work of my air filter unless the staining you see in the pic is to be expected? There is some black smoke at high revs in a short burst in neutral but not enough to have worried me.

McCabe-Thiele (Ted):
Does make you wonder if it might be easier to vent directly to atmosphere.

Laverda Dave:
That doesn't look good. Do you have the piece of foam between the strainer and filter housing (the air filter sits on it and it's held in position with a large crosshead screw. If you don't have the foam the oil gases will blow straight over your filter. It does appear as though the engine is breathing a bit heavy. Are all the breather hoses correctly routed with no kinks? Make sure the large breather hose that runs down the back of the engine is located correctly in the cast boss of the engine case in front of the swing arm and has not been caught between the swing arm and frame as happened to me many years ago.

Athame57:

--- Quote from: Laverda Dave on August 16, 2023, 02:51:35 PM ---That doesn't look good. Do you have the piece of foam between the strainer and filter housing...

--- End quote ---
Yes, I got it from Julie actually. The bowl below it I didn't have for months when I first got this bike five years ago, I had to scour the globe for a long time and suddenly there it was staring back at me on the 400Four bits site. I do squeeze out the tip of the breather drain pipe but I see your point about it being snagged, but the lack of pooling suggests it will be ok when I go to look proper, we'll see.

Athame57:

--- Quote from: McCabe-Thiele (Ted) on August 16, 2023, 02:49:04 PM ---Does make you wonder if it might be easier to vent directly to atmosphere.

--- End quote ---
Well, I certainly started like that in the first months, the whole system was missing.... no risk of lost pressure et al?

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