how much oil in air filter


How much oil do you guys use on your air filter? I just cleaned mine and used some PJ1 super tacky oil and mushed it around in a plastic bag until it was good and covered, squeezed out as much as I possibly could and then wrapped it with a towell and squeezed it again. There is still plenty left on the filter (it's dark red so it's easy to see on the yellow filter). This used to work fine for my old 2-stroke, but I'm sure this thing will suck more air than my old bike so I don't want to leave enough on the filter to get sucked in. Is this about the same as you guys do? I have to find a neater way to do this. :)

An unusually cold morning and an over-oiled filter ruined a day of riding for me. I never got away from where we were parked the whole day, all because the motor sucked the filter oil into the carb. Trying to clean and re-oil a filter in a dirt parking lot with only gasoline and motor oil isn't a fun job. (Of course, I dropped the damn thing at least once.)

I usually spray a light coating of aerosol PJ1 air filter oil on the inside and outside of the filter and knead it to distribute the oil evenly. Then I let it sit overnight before I put it in the bike. This time my thoughts were "I'll just put some extra oil on the filter, it couldn't hurt..." Famous last words. There was just enough oil in the filter such that there was a very small amount of oil "pooled" in the bottom of the filter. Not enough to drip or wring out, but gravity had settled it out just a little. And I had let it dry out overnight before I ran it.

I have oiled my filters a hundred times on this bike and had never had a problem except this once. When I got home, I had to take apart and thoroughly clean my carb before the bike would run again. And I had just read how the YZ/WR 4XX series engines require a lightly oiled filter and to not put in a freshly oiled filter until it has "dried".

It was a lesson I won't forget.

BTW, I always assess the condition of my air filter when I take it out for cleaning. Even when it is filthy and black on the outside, it always looks spotlessly clean and pink on the inside, so I guess light oil works. (I use Twin Air filters.)

Here's what I do and it seems to work for me.

Go get yourself another filter, be it a Uni or a Twin Air, both are just fine. Oil them both at the same time. I use Uni Filter spray on foam filter oil, but any quality foam filter oil will be just dandy. Make sure the filter is DRY. I spray the stock filter thoughly on both the inside and outside and knead the oil around so the thing is good and saturated. On my Uni filter the thing is a two part filter with dual density foam, and I do the same thing, spray the insides and outsides of each, make sure the oil is applied evenly and put the two filter halves back together. Then I install one at least two days before I ride. This lets the oil settle and won't foul any plugs.

The spare filter gets used the next time I ride, and because it's been oiled so far in advance I can just install the thing and go. I keep the spare filter in an old cookie jar, which lets in enough air (and the occasional bug) but keeps dust and stuff off the clean and nicely oiled filter.

I also, before installing the filter, grease the seal that mates the filter to the airbox surface.

Lastly, and although I've never fouled a plug on my bike, keep an extra plug with me. Just an old habit from my two-stroke days.

I agree with the Husker, having two filters is key. You may tear one at some point, I rotate them so I never have to oil a wet filter or ride w/ a freshly oiled one, although doing the latter has never caused me any problems (w/ PJ1 filter oil).

I always used to grease my filters where they seat with the box but IMO the Yamaha airbox setup seals very well and this isn’t really necessary. Just my opinion. But I do put a dab of grease on the center hole, I’ve noticed dirt trying to work its way down the bolt hole in the cage, and of course I make sure the filter is completely oiled like Husker describes, especially the lip.

Hope this helps.

I use filter skins and only clean my filter about once every 8 months or 30 rides or so (but I think that's overkill), so I've never had an over oiling problem.

I can feel the flames coming........whew, it's hot in here.


I'm with Husker and Hick. Having two or more filters is the key (five or six in my case). I clean/dry them all at once and then have an airtight container with a couple of quarts of filter oil in it. Then dip and sqeeze the extra back in the container. I've never had a prob. with fouled plugs due to too much oil and since I've been using the container I waste far less filter oil.



99 YZ400F, 86 XR250

76 RD400, 71 Z50

I went and did it, and I knew better. Preparing my WR for a dual-sport weekend, I did all the usual maintenance, including cleaning and re-oiling my air filter(s). I sprayed a LITTLE too much oil on my air filter. It ran, but it was weak on the top end, harder to start cold, and backfired on deceleration. It also sputtered before it finally would clean up in the mid range. I had a feeling it was my air filter, so when I was cleaning the bike this evening, I took off the filter and ran it for a few minutes. It was clean on the bottom and strong on top like it's supposed to be. Luckily, it didn't suck any oil into the carb and require a disassembly and cleaning. I guess there's a fine line between too much oil and "just right."

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