stuttering at low rpm's

[jan.van.gent]

[quote author=jan.van.gent link=topic=22602.msg260793#msg260793 date=1495090886]
[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 [size=1em]being your problem, it could be something else.  Tell me more if there is any more?      [/size]


[/quote]
I rebuilt the lower end of all 4 carbs. Thus replacing the neelde valve, the needle O-ring and the needle valve seat and the float chamber gasket. I believe one or more of the neelde valves were not closing properly, + the float chamber gaskets which were quite brittle ended up in leaking carb(s).

Would a blockage not rather cause a fuel shortage instead of to much fuel?
What do you mean by enricher circuit? Is this linked to the choke? Or? What to look for in the manual (http://foc-u.co.uk/index.php?action=down...nfile&id=8) ?

Thank you very much for the input!!