if any small part broke off at the top of the piston, you would undoubtedly hear what sounds like a rod knock with the piece hitting the head There is really not a lot of clearance in there The plug would most likely have the gap closed by the banging and the engine would run weak from the remaining three cylinders
Common problem with Weber carbs is the the studs and washers holding the air cleaner in place will rattle loose and lay in the secondary side of a 32/36 until you step on it opening the secondary The nut and washer particularly will embed in the top of the piston and create the havoc you describe Ask me how I know . I did this twice on my Dad's Ford Cortina with a weber 32/36 The fix is to take the head off, Remove the offending pieces and put it back together again There is only a very low probability that you have hurt the crank the rod or the piston
First check to see If you have any nuts and washers missing from your carb If they are all in place ,Well it's a bigger issue I think you could pull the plug without damage but why bother because you will need to pull the head to see what's happening and go from there. There are most likely suggestion's about this procedure here on the board My only suggestion would can pull the head with the intake and carb and the exhaust attached to save some reinstall work This works well if you use and engine hoist to pull the head and manifolds attached. I have one to loan you , and I'd be happy to help if you need me.
Lets hope its something simple