OK Gents...here is a ligit question for you guys using 20W50 do to the "heat" outside. What is the temperature that you feel you need to use 20W50 vs like 10W40? And I still use the dino oil here in WI. And don't be a smart a$$ and tell me to use the search button. 
I'm sure this will be an unpopular post. But, whatever. Instead of using the search button. I looked at a few of the owner's manuals that Honda distributed with the bikes when new. I know that most most don't believe Honda had a clue what was best for their engines. So, those people can just skip this post as being irrelevant.
Anyway, the 72 Cb 500 manual says to use 20W-50 oil when temps are above 59F or 15C.
By 1974, when the 550 was introduced there was no further mention of 20W-50. But, at temps above 59F it say to use 30W or 10W-40 (for all temperatures).
The '77 Cb750F manual hadn't changed from the 74 CB550 recommendation shown above.
For fun, I looked at the Shop manuals, too. (Hey, I was at the dentist this morning. So by comparison...)
500/550 shop manual does state 10W-40 or 20W-50. This is in the maintenance section that was first published with the CB500 offering.
In the troubleshooting section, pg. 129, it lists a trouble as
"Difficult gear shifting". Cause Number 6 is
"High oil viscosity", with a remedy of
"change the oil"I must say that I found my 74 Cb550 a bit harder to shift with the Castrol 20W-50 oil I tried a few summers during it's life. It shifted better with 10W-40, and even better still with Honda's HP4 semi-synthetic.
I looked in the 750 manual and found 40W/50W recommendation. But, then I noticed it was for the headlight.
Moving on...
In the periodic maintenance section Pg 178 it also lists 10W-40 or 20W-50. Probably first printed about 1969-1970-ish.
On page 231 (supplement to CB750F) it specifies 10W-40 oil, with a distinct absence of a 20W-50 reference.
Maybe Honda learned something about the 20W-50 recommendation and changed it?
Maybe it only applies to a bike with the stock air box and tires?
Cheers,
