What Allen said ~

The nature of detergent oils is , the detergent , when  its hot (not just warm) keeps the dirt & bad stuf , suspended in the oil so the filter catches it , and so it drains out when you drain the oil .

Engines , (any engine) should always be fully warmed up when doing oil changes ~ for Motocycles  it's easy to lay out your tools & drain pan on a weekend morning then ride to breakfast and do the oil change the moment you get back  or ride it to work and rain when you initially get home ~ doing it this way actually cleans out the inside of  the engine after decades of deferred service ~ I pretty much only buy junk so I get to see first hand how the black crud that's stuck inside the engine , dissolves as you ride it and do proper , blistering hot oil changes .

All vintage Honda Moto engines have nifty centrifugal oil filters on the end of the crankshaft and the one inside every CT90 is usually packed full of sludge .

Your cute little Honda is a finely designed and built machine ~ if you take care of it , it'll take *very* good care of you .