LINK TO YOU TUBE VIDEO
https://www.youtube.com/watch?v=T8M-m0i3uWIwas sound there before the spring gear was changed new gear will whine against an old gear
and straight cut gears whine unless running in lots of oil
but if sound there before i am thinking air leak somewhere
running a bike at very slow rpm is hard on them
turned (flipped)around several old /2 BMW's for a profit
the guys pounded the cranks out of them by idling them too slow
in fact the word slow does not do it justice ..they were some where between stopped and very slow
i bought an r50 s crank from brown motor works in ca usa in 1975 it was $1500 usd almost enough for a new 750 Honda 4
and my dad was good at fixing old BMW cranks but i never got the hang of it
and lot of noise can be by not having a stock air box
my 660 is missing one of the plastic covers under the seat an its loud
any one with 4 and 5 as extra in the parts box i am interested .. number 2 the air filter is not found in USA
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