Engine sound will increase a little but no need to worry about that.
You have many options available for carby cultus.
SGO Premium 10w40 api sg.
ZIC A 10w40 api sn.
ZIC M 15W40 api sj.
Shell 10w40 or 5w30 etc... If engine is strong enough.
Actually in this engine api grading doesn't matter a lot due to some circumstances......
If you are reluctant to go for thinner oil's then give ZIC M 15W40 a try.
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