Okay, so I'm in the phase where I'm dialling in the carb on my '76 DT 175 and I'm out on the road when I realised something...

I've never ridden a 2-stroke before!

I've ridden 4-strokes: 50cc scooters, 125 "learner" bikes and "proper" bikes from 400 to 700cc. TBH, none of those ever really required any thought

This is what I've worked out so far: the bike likes to go about its business at >4k all the time which is a bit disconcerting drum brakes require forward planning and engine braking is no longer a thing. (I can appreciate that drums + beast slumbering under 4k would translate to excellent technical efficiency on trails, trials and so forth but I'm just out on the road at the moment.)

I'd therefore appreciate any tips for a new-to-2-strokes rider. YouTube vids aren't terribly helpful as they all seem aimed at modern dirt bikes. For example, one tip is that you don't need the clutch to change down, only going up and even then a skilled rider (not me obviously) might not bother. Does this apply to my old DT? Or only after serious practice?

Read the owner's manual.

Always use the clutch.

(When racing, we used to shift up and down without the clutch but it can be hard on parts... one thing some of the Yamaha models were good about was you could upshift without the clutch under full power... no backing off the throttle... but just because you "can" do something, doesn't mean you "should")

Eazy-X, your post reminds me of the time that I had the opposite "problem"!

My first three years on bikes were spent on two strokes - first up a FS1E moped and then a RD125B.

I passed my test in 1981 and it was time to move on up! I really wanted a RD400, but, as there were none to be found in or around Salisbury at the time, I ended up buying a Honda 400/4 from Romsey. I close the throttle approaching the first major junction on the ride home and, because of the 400/4's engine breaking, end up stopping about 100 yards before the junction! I couldn't stop laughing! Mind you, the amazing sound that the bike made on the overrun with the Dunstall Decibel "silencer" that was fitted was something to behold!

Glad you're on the road now.