Piston Skirt

Nope The original issue was unstable idle in certain conditions. First it was corrected by changing purge bulb with tighter return valve (went from standard orange to special black material), but later it was changed to active idle control altogether. Presence of that system can be recognized by PI (Programmable Ignition) symbol next to laser etched S/N, X logo on the starter logo and D-shape idle screw (as it is otherwise useless for untrained person without carb tools anyways).

The X logo appeared together with updated ignition module (the one with active idle control). Carburettor changes were non-essential.

There is nothing in this "farmer 40cc size" that is lighter. 3510 is much lighter and has some fun factor to it, but less powerful.

It was, but CS-420EMS is discontinued.

3510AC and 4010EC have separate electronically controlled fuel passage to aid starting (4010EC also uses that for better/faster engine warmup and acceleration at all temperatures). Both use "manual" regular carburettors that will run even if you disconnect the electronics aided part.

Glad to help The US and non-US versions (and certifications) usually differ, hence the differences in certified bar manufacturers and lenghts as there are some differences in requirements and testing procedures. Originally this chainsaw was designed around A4S chain hence it performs the best with narrow gauge 1/4". The 3/8" laminated Tsumura is somewhat "budget" version. Here are the official sizes from catalogue (20cm is 8", 25cm is 10"):

It is IPX4 certified.

Butterfly type carburettor L controlled ports (3 little ones) are always influencing engine work. At idle usually the closest hole to the engine is open, but starting from acceleration process and up to WOT it sprays fuel from all 3 L ports happier than a race winner sprays champagne. L adjustment always has influence on all RPM range. It is just felt differently on different engines, depending on many factors.

The myth about pencil and NASA has long been debunked. For those "Soviets safer than NASA" I recommend first reading on N1, R-16 and similar rockets and catastrophes. Anyway it is better to get back to the topic.

There is not much extra simplicity in comparison except there is one less solenoid block, wire loom and extra power generating unit. This saves some ~100 grams alone. The lower weight comes from that and from the engine/crankcase design. Actually the push-pull pre-filtration system and oil expansion chambers are a bit more advanced than those found on competitor models so except auto-tune there isn't much where is less techy. Any modern chainsaw model (except those with shady origin) has to pass exactly the same ISO tests for loads from all sides and dropping, so the durability part of the story is a bit of an urban myth.

550XP says 859, but that's apples to oranges as it's major difference in ccs and ultra-major in weight especially if you add the UL Sugi bar which comes stock. Hell, it's even cheaper than 540iXP. MS 241 from the same class is 864 so it's hard to understand where you want the titanium Probably you just don't need 40cc class saw

How much are 543 nowadays in UK?

Understandable. Yet US normally has generally different products and even average American user will normally have different preferences (see lawnmowers, hedge trimmers and even chainsaws of any manufacturer). UK has more in common with Europe so it’s understandable the range and even safety requirements for double insulation is different.

What was/is the issue?

Some of those you see on YouTube in US got there from UK, actually And the most shown one was smuggled to US from Germany. I also see northeast side of Europe selling them for a while already. And it’s hard to forget all the supply mess, especially when other manufacturers wouldn’t even have batteries for most of 2022 worldwide…