Crankcase breather question.

Ok here's whats happening; After long freeway runs at speeds of 70+,(I'm commuting 140 miles a day), I'm getting alot of oil in the airbox which then drains out in front of my rear tire and all over the exhaust.
Ok here's the question; What is causing the oil to pass through the breather in such larger quantities? I drained the oil and refilled with the correct amount,( I had this happen once when I had overfilled it.). It happened again after changing the oil. I know that there is a large amount of pres. under the pistons at higher rpm and of corse the airbox will be under a vacume but shouldn't the breather filter out the liquid oil and only pass the vapor or mist through? BTW the engine is stock, with the stock airbox, breather, carbs, etc. Just a K&N stock replacement airfilter,( now an oil bath filter LOL!).

sounds like a blowby issue,does the motor smoke?a little oil is normal but a oil soaked filter is not a good sign.

It smokes a little out of cyl #4 when cold but cleans up quickly. The bike had sat for 2 months while I waited to put new chain and sprockets on it. I thought maybe the oil had drained from the top end and when I started it again, the oil level in the crankcase may have been too high causing the oil to pass through the breather the same as an over fill condition. I'm riding my Yamaha at the moment so I can take my time to figure this out.

On mine it's a blowby issue... Have the whole topend off right now... Same symptoms though, hard running always does it. Worse when I fill the oil to top of recommended level. installed an oil pressure gauge ($25 bucks or so) a while ago. At idle my crankcase compression is supposed to be around 3 psi. I am running about 6...

Get a compression tester and do a dry then wet compression test. Sounds like it is time for new rings or possibly pistons/rings if the clearance is outside spec.

Do a wet/dry comp test to see if blow by is an issue. In the mean time route the airbox hose AWAY from your rear tire. Or disconnect breather from airbox and route over chain for some free oiling.

I like the chain oiling idea!

I believe the first models of Z1 came with a small oil pump to do just that lube the chain.

Question ?
Are you using a motorcycle rated oil?
If not change it to one (bikes DONT like new car oils)and see if it helps.
Do you have anything under your seat (gloves/shop towel)costom seat ? Anything that might be messing with free air flow into your airbox?
How do your spark plugs look?
Have one "funny" looking one ? If you do, switch holes with a good looking one and see if it cleans up and the good one starts to look "funny".If so ,you found the hole where your problem is.
Compression tests are ok , A leakdown test is MUCH better.

And by the way ,clean your K&N ,pull it out for a few days or put in a stock one untill you figure out whats going on .
An oil soaked filter WILL drive you nuts.
They work best with very little very sticky oil not LOTS of just oil.

And by the way ,clean your K&N ,pull it out for a few days or put in a stock one untill you figure out whats going on .
An oil soaked filter WILL drive you nuts.
They work best with very little very sticky oil not LOTS of just oil.