By chance I glanced at one of my Atco 2 strokes this evening as I went into the garage with a new bag of Growmore...
The Atco I refer to here is the oldest of the two...it came from a, now sadly departed, next door neighbour. The very neighbour who I used to "help" mow the lawn...in a time at the very start of my recall.
He used to operate the mower but left one handlebar free for me to hold as I walked alongside.!...happy days......
I used to listen out for the unique sound of the kick start as he coaxed the mower into life...and then would dash to Mum to ask if I could go and "help" Mr Farmer with his mowing...
His Atco had cast aluminium handlebars....a different style, wooden ?, was used on the later 1950s ones.?
The earlier mowers had adjusting screws, back and forth, to pivot the bottom blade unit. I also have a later one that had a strange system of moving the bearing block to adjust.
After mowing Mr Farmer always used to turn off the petrol tap and allow the engine to run to a stop...on low revs..I add. This, he told me, allowed for a clean start next time with empty crankcase and fresh fuel mix in the carburettor too.
The slide and needle should lower down in the carb barrel to allow slow running. I don't think there is any throttle stop that the slide sits down onto.
One thing that dear old Mr Farmer used to do was to run the engine with partial choke..this in effect then limiting the engine from racing if the throttle was opened right up....there being no engine governor..only the one walking behind...or alongside..
Not a definitive answer...just another of my reminiscings? again..