Carb adjustment limiter?

[Matt_Harrington]

I understand what the little plastic (?) adjuster limiter (that covers the mixture screw) does but every set of carbs I have seen seems to be missing them. Is there a reason or is it one of those things that the items are not necessary? Or get lost at service time and never replaced? Just a thought!
Matt

[Nurse Julie]

Lost, not replaced as not necessary.

[McCabe-Thiele (Ted)]

Not essential but it does stop you turning the screw too far as it restricts the adjustment.

[Bryanj]

Part of emmission regs need to be put in file 13 under B for bin

[Cappodimonte]

The black caps were used for aesthetic reasons, in that plastic does not tarnish as the underlying brass screw would. The second reason was to dissuade owners who ‘tinkered’ with settings not to do so as removal of the cap could easily be seen and warranty voided.
The capping of adjustments was considered necessary by manufacturers as there were plenty of so called ‘Tuning Expert’s’ who’d fiddle about not knowing what they were doing and making things worse.
This I know from my Motor Vehicle days where a car would come in running badly, you’d fix the problem. Owner would take it away then come back the next day complaining it was worse than before. It was clear they’d buggered about with it so I took to painting any adjustment screws which would immediately show up if they’d been tampered with.
I’d confront customers who’d obviously deniy  it, so they’d either have to pay or take it away running badly, soon stopped them, yes I lost a few customers but I never lost sleep over it as they were wasting my time and my money.

[Matt_Harrington]

As I thought - I'll bag mine up and put away for posterity!
Matt

[K2-K6]

I feel there's more reason behind them fitted to these bikes.

We are viewing them from our small island location, along with it's very moderate altitude and hence barometric pressure range.  All other elements being equal, the adjustment offered by this circuit is to accommodate that pressure change in different market conditions ultimately.

Colorado for example has average 2200 mtrs (I'm only aware of this in fuelling terms from working through a mixture problem with someone living there on a fuel injection system) and would need significant shift in idle mixture to avoid rich running engine. It's a massive difference on a small motor like this to have it run properly.

If you needed to do this on the fly, travelling interstate for example, then convenient stop position of that screw would be highly desirable attribute. 

If anyone has read "zen and the art of motorcycle maintenance" it uses exactly this adjustment to forward its contrast in teaching methods:- are things taught in absolute to pass exams (the academic view of some and core tenet of the book) or do you teach vocational strategies (think apprenticeships etc) that allows the recipient to really use and understand systems placed in front of them.

The protagonists, one can adjust his own bike and fix it as they journey across America, the other needing to go to a shop to deal with problems as they arise.

Just view from wider appreciation than a narrower UK centric experience.

Incidentally, I've seen a few times in France a locally registered 500 Four living at about average 900mtrs altitude that would likely be set different to the ones on here, within easy range of the coast Mediterranean too. It would be much easier to have positive stops rather than getting reference from turning right inwards and then doing the 1/2 turn, one turn, one and a half, one and three quarter dance each time