What oil did you use as the wrong oil used and over fill will do this ,
This is the oil needed and amount .
The YD 25 use castrol Edge 5W-40 and use no more than 6.4 litre with oil filter change
and 6.4litre with out filter change .
If you have Overfilled then drain off the amount of oil needed to get it to the right level .
Too much oil in an engine is just about as bad as to little .
Please take care when draining off oil, as it may be very hot and will burn and scald your hands .
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Kindest regards Greg