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Does anyone know what this pipe is for, or where it goes.
I know its the return from the oil/air separator in clutch housing but why does it connect to this pipe. It looks like the pipe goes into the sump, why not just empty into clutch housing and drain into sump with rest of oil. ? There's an oil way to sump in casting right next to it.

Des

Would it be that if it discharged back into the clutch casing then the oil would be picked back up and thrown into the separator time after time ?

With it returning via the tube it gets a chance to remix with the oil in the sump and further air bubbles are eliminated.?

If the oil is frothy prior to the separator and then flows through it and straight back to the clutch and frothed again
at some point the separator must be unable to cope as not all the air bubbles will be removed at each pass and must accumulate.?

Does the separator also act as a reservoir/funnel for the treated oil and allow it back into the sump at a controlled rate via the tube rather than letting it splash straight back at the clutch and exasperating the issue ?

Just musings but there will be a reason; very rarely did Yamaha do unnecessary engineering

Not sure....I've got my 88 in bits just now and there is no pipe in mine..

Hi thanks for reply's

Mine is an 89 exup so must be different

I think Ive worked it out?, the pipe is a breather pipe for the sump. The sump cant breathe through the casting hole due to the oil in clutch. The breather goes into the clutch case air/oil separator which also connects to the crank case breather at top of case.
So the air is drawn from the sump and clutch ( the air is separated in the clutch case labyrinth ) into the crank case to the carbs.
Oil from clutch labyrinth will return via pipe as this needs to be sealed from oil in clutch case.

Hope this make sense ?