I do not know where is the oil filler cap?????

All questions need FULL 'make model (what is is)', or we guess.

Let's guess it is a Stihl. The part is in the link.

Or you can Google

make model bar oil filler cap replacement

or

make model replacement parts

https://www.google.com/search?q=380+Chainsaw%2C+Filler+cap+for+bar+oil

..

Oil cap leaking - Harley Davidson Forums

www.hdforums.com/forum/sportster.../550364-oil-cap-leaking.html

Aug 13, 2010 - There is always a big amout of oil at the bottom of the bike (probably all from oil cap) and it's drippin' all the time especially if bike is hot. 2007 sportster 883 leaking oil
May 31, 2009
Sportster Oil Leak
Oct 3, 2006
More results from www.hdforums.com

Oil leak at filler cap - Stromtrooper Forum : Suzuki V-Strom ...

www.stromtrooper.com/v-strom-service.../78495-oil-leak-filler-cap.html

Aug 24, 2012 - but more so it seems to me that a new bike shouldn't be leaking oil at all. ... Do I just need to have the dealer replace the seal on the filler cap?

Harley Davidson Motorcycles : About Slobbering Oil ...

? 2:20
https://www.youtube.com/watch?v=lB2DpvxKTGw
Dec 1, 2008 - Uploaded by expertvillage

Need to know what kind of vehicle.

Well -doing that sort of takes out the PCV System
doesn't it

Unmetered air comes in the oil fill hole & gets drawn into
the intake & leans out the fuel mix

You also got PCV system issues with high vacuum

there shouldn't be a filler tube, just a dipstick tube for checking the oil level. to put the oil in the engine, there should be a oil cap on the right hand side valve cover. if the dipstick tube isn't there, you definitely need to get one from a parts yard or store, you can be losing oil from the dipstick hole that goes to the oil pan...

Do you know where the oil filler cap is ? if so look to the left of the oil filler cap. if not lower right side last cover to the left take out the 2 allen bolts to remove cover.

Gasoline only usually means 4 stroke.
2 stroke requires a mixture of gasoline and 2 stroke oil'
Look for an oil filler cap on the equipment, no oil filler cap means 2 stroke.
If you have an oil filler cap there will be a dipstick therefore your kit will be 4 stroke.

Hope this helps'
Chris.

This is normal. With oil filler cap off, the vacuum pressure in the engine is lowered.

Charlie

The engine breather pipe seems to be blocked.
It may also damage the oil seals.

1.You must have the recommended number of liters
of oil replacement in your position.
2. Locate the oil drain plug. This is either at the side
or at the the bottom of your engine.
3. Open the oil filler cap.
4. Unscrew the oil drain plug counter clockwise and
allow the engine oil to drain until it stops dripping.
5. Screw the oil back in place tight. Fill it up with
the oil replacement at the place where the oil
filler cap was placed, up to the point of maximum
oil level.
6. Replace the oil filler cap and close tight..
replac