I've looked into this a bit more since my first post, the information I posted earlier came from a 1963 Driver's manual for the C72/77. This describes HOW to clean the filter but doesn't tell you how often to do it.
As Tom has pointed out the 1966 CB77 manual suggests cleaning the filter at 1800 miles then at 4300 miles (2500 mile intervals?) and I've found this same information in my 1965 CL77 Owner's Manual.
Another, undated but I think earlier CB72/77 Driver's manual recommends cleaning the filter after the first 2000 miles and then every 2000 miles thereafter. Strangely, these later three manuals tell you HOW OFTEN to clean the filter but none of them tell you how to do it!
It could be that Honda discovered that the method they printed in the early C72/77 Manual was almost impossible to do as described so didn't print it in later manuals.
Somewhere, I have a period road test with a picture showing that the tester has removed to oil filter cover and drawn out the centre spindle to show how easy it is to clean the filter, the article doesn't say how or if he got it back in again!!
In answer to the original question I think the best idea is to clean the filter and then do it again after say 3000 miles. The amount of new sludge build up then will give you a good idea about if you need to clean it more or less often, assuming that you stick to a similar oil of course as oil choice might affect sludge build up.
C72 oil spinner location - and how to clean it!Re: Oil Filter cleaning.DJM
Good info and advice. Judging from the filters I have dismantled, it was just too much effort for most owners. Did you see the pictures I sent of "Trevor's" bike? In here..... https://www.flickr.com/photos/63154743@ ... 5487199755 Odd choice of front fender....... G
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