stuttering at low rpm's

[Gnasher]

[quote author=Gnasher link=topic=22602.msg260782#msg260782 date=1495059469]
It's a fuelling issue, too late now to go into detail will tomorrow.

I agree, looking forward to hear more about it
What to look for/replace/...?
[/quote]

Ok, based on your post I’m assuming a few things here so this may not be correct: -

1.The cylinder giving trouble has the carb you rebuilt, or did you rebuild them all?
2.Plus you state everything runs fine at high rpm/big throttle positions, if it was the HT circuit it would usually be the opposite.
The part of the rev range you’re having issues with is just past  pilot circuit, this now points to several possible problems: -

1.Pilot/Main jet damage/blockage
2.Needle height setting
3.Enricher circuit jammed/blocked.

Your leaking crab would have had nothing to do with shot rubbers, but rather worn metering valve/jet, stuck/damaged or wrongly set float height.  When you “rebuilt” the carb what did you do?

Your black plug is over fuelling, i.e. too richer mixture which can be any or all of the above.  If you rebuilt all the carbs and it’s not the one that was leaking, it’s still very possible you didn’t assemble one of them correctly,  there's crap in the pilot circuit or you missed something like jammed enricher plunger.

Personally based on what you’ve said and what I know at present I’d go for No 3 first check the plunger is not stuck out, then No 1 as being your problem, it could be something else.  Tell me more if there is any more?