Michel,
I am not sure if the answer is clear, but the needle valve in the filler neck will not shut off the flow of oil to the chain oiler, it will only moderate the flow, but this is sometimes enough to reduce the oil flow that runs by the tube that goes to the chain oiler. This is because, as Greg mentioned in another post, the chain oiler cannot be closed from the tank filler end. If you look carefully at the square block brazed into the filler neck there is a hole drilled through the timing side of the square block that goes right to the chain oiler tube and bypasses the metering needle.
So, oil can find its way down this open hole that goes right to the chain oiler even with the metering needle closed. It is more usual that air rather than oil can find its way through this hole (if the metering needle is closed) and this hole could easily be used as a breather for the oil tank. If too much oil does find its way down the hole with the metering needle closed also it may be best to block the chain oiler at the rear of the UFM by blocking it with an A26 plug as Russell mentions and several others (including me) have done. You might find some oil weeping from the vent on your oil cap after doing this, but that rarely happens.
David
I am not sure if the answer is clear, but the needle valve in the filler neck will not shut off the flow of oil to the chain oiler, it will only moderate the flow, but this is sometimes enough to reduce the oil flow that runs by the tube that goes to the chain oiler. This is because, as Greg mentioned in another post, the chain oiler cannot be closed from the tank filler end. If you look carefully at the square block brazed into the filler neck there is a hole drilled through the timing side of the square block that goes right to the chain oiler tube and bypasses the metering needle.
So, oil can find its way down this open hole that goes right to the chain oiler even with the metering needle closed. It is more usual that air rather than oil can find its way through this hole (if the metering needle is closed) and this hole could easily be used as a breather for the oil tank. If too much oil does find its way down the hole with the metering needle closed also it may be best to block the chain oiler at the rear of the UFM by blocking it with an A26 plug as Russell mentions and several others (including me) have done. You might find some oil weeping from the vent on your oil cap after doing this, but that rarely happens.
David