Oil In Air Filter

[Slydynbye]

Well you live and learn.
Any idea why two pipes come back from the carbs to the air box, although if there's the sub air filter it's probably viccy verca, that is from the air box to the carbs. Is it some sort of balance?
I stand by to be edumicated.
Upt'North.

I think it might have something to do with North American emission control systems, but that is 100% a guess. I have attached a picture of it.

Michael

Sub-Air Filter Assembly - ST 1100
View attachment 259192

Are you saying you don't have this in Europe?
There is a T fitting between the carbs that connects to both carbs, it enters the carb within the chamber just below the Vacuum piston diaphragm. My guess is it either balances the pistons, allows them to move freely, or is a path for vacuum intake.
If the Sub air filter disintegrates you will find the little bits inside the carb there. Here's a picture

 

[martin cullinan]

Hi Martin:

Welcome to our forum community!

As others have mentioned, a small amount of oil residue in the air filter enclosure (and on the filter itself) is normal, it's a result of vapours coming from the breather.

If the bike has ever tipped over to 90° or more with the engine running, a LOT of oil will go up the breather hose into the air filter.

Note the picture of my bike above my name on the left hand side (the avatar) - when my bike rolled upside down into the ditch, a lot of oil got into the air filter. When I started it up, it smoked like a destroyer under attack in a WW II movie. I then rode about 300 miles to the city limits of Zurich - no problems - until I hit a big bump in a construction zone on the expressway, which was sufficient to bounce all the loose oil on the bottom of the filter enclosure into the carbs. There was a big Mercedes S right on my tail, about 30 feet behind me, and he just disappeared in the cloud of smoke... when the smoke cloud cleared, I could see the Mercedes far, far behind me, the windshield wipers and washer going at full blast trying to clean the mess of his windshield... it is the funniest thing that has ever happened to me while riding the moto.

I bet he figured I had some kind of defensive smoke system installed - I also bet he has never tailgated a motorcycle again since that day.

Michael

Somehow I reckon the driver of the Merc learnt a huge lesson that day!! Thanks for your advice though. I've ordered a full service kit and I will be also checking, and changing if necessary, the air sub-filter. Safe riding sir!

 

[CYYJ]

Hi Martin:

The sub air filter is a tiny bit of foam, not much bigger than a large postage stamp, and only about 3mm thick. It's a 10 second job to change it, assuming you have the false fuel tank cover off.

In 200,000+ kilometres and 20 years on my ST 1100, I've never seen that little filter get dirty, but I change it about once ever 4 to 5 years because it will start to break down and disintegrate if it is left in place longer than that.

Apropos of your original inquiry about oil in the (main) air filter, or on the inside of the air filter housing: there is a breather hose that connects to the underside of the bottom half of the air filter housing - the connection is at about the 1 o'clock position if you are sitting astride the bike. That leads up into a little walled-off compartment that is open at the top to the main air filter housing. That's where the oil comes from, up that breather pipe.

If my memory serves me correctly (I'm at home in Canada, I left the bike in Tunisia this spring when I fled home at the start of the COVID pandemic), it's pretty easy to remove the bottom half of the ST 1100 air filter enclosure. If you so desire, you could remove it, wash it out, and then you would be starting with a "clean" enclosure that will allow you to monitor future oil buildup.

Before you do that, though, you need to go buy a JIS (Japanese Industrial Specification) screwdriver. The screws on any Japanese motorcycle that you think are Phillips head (cross head) are not Phillips, they are JIS. If you use a regular Phillips screwdriver on them, you will eventually chew the heads up. See the PDF attached, which explains the whole story better than I can.

You can find these screwdrivers online - it's rare to find them in shops. Vessel is a trusted brand. It's best to get two sizes, medium and large - no need to get the tiny ones. There's also a discussion here in the forum about where to get JIS Screwdrivers: Vessel 220W Ball Grip JIS screw driver

FYI, JIS screwdrivers work great on Phillips head screws, but not the other way around.

Michael