Odd oil-change situation.

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I've gone back using 10w-40.

All is normal agian.


THANKS!

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OK, had Mystic synthetic oil 20w-50 for a year.It ranfine but as the 20,000 miles grew so didengine noise. (used Mystic from 58K to 78K)

___ Symptoms:
Clutch out, noise, pullin,none.
Tappets tinkled a little.
A type of "primary chain" whirrring sound.
FELT a slight random knock in the handle bars.
On acceleration, felt sluggish even when warm (20w-50).
Shifting gearstook some energy & was difficult to shift smoothly.

Changed the oil to non-synthetic.Used a cheap house brandof 5w-20 for thefirst flush. I planned a short ride maybean hourto flush the tappets and the followinghappened.
___ Symptoms:
Clutch in or out = no noise.
Tappets the tink was gone.
NO more type of primary chain whirrr, not even a whisper.
Random knock in the bars, GONE.
On acceleration, OODLES OF POWER! (probably the thin 5w-20)
Shifting,seemed to pre-think what gear I wanted & did it without effort.


So I kept this 5w-20 oil in for couple moredays of testing. I could not believe howfast, smooth & quiet it ran. On day 3,I change to 20w-50 using thesame brand ofcheap house oil as the 5w-20. 75%of the originalsynthetic symptoms were back though not quite asbad.
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The Wings motor is aclose toleranced machine and with the5w-20it ran like a freshly rebuilt Singer.

Any suggestions as to why it ran so well with 5w-20?
Anyone havesimilar situations like this?
Should we be using 5w-40 or 5w-50 in our Wings?
Pros / Cons?