Bro, 20w-50 is an extremely thick oil for your engine. 0w-20, 5w-20 or max. 5w-30, API SN / SN Plus are the recommended oil grades for 660 cc engines.
I would suggest to immediately switch to any of these oil grades, and if you want best for bucks, go for:
ZIC A+ (in 5w-20) or Total Quartz 9000 Future Series (in 0w-20 and 5w-30).
In 0w-20, many brands are available, you can choose anyone if going for 0w-20.
Which ever brand and oil grade you choose, just ensure that it's fully synthetic and
% genuine and original. Just change oil along with genuine, OEM Oil filter after every 5,000 Kms, and you are Good to go.