what does the plastic plug over the pilot jet do?

Last evening i dove into cleaning/replacing parts in my 83 gpz 550 carb's, one thing i noticed were plastic plugs with a small o-ring on them that were over the pilot jets, I've never seen this before. I tried to replace the old o-ring on one of them from the k&L kits i purchased but with the new o-ring the plug wouldn't fit into its hole, i ended up trimming it down with a razor to get it to fit, i went ahead and left the other 3 alone, however they don't fit to tight in the hole, i hope this wont create a problem, i do see there is a stem in the float bowl that helps hold these plugs in place.

I think the way the pilot passages are drilled, the plugs are needed for the proper uptake of fuel.

A metric nitrile o-ring kit might have a size that will work. or viton o-rings. Kits are available at HarborFreight or eebbaayy or etc. If they still won't fit right & a good substitute cap couldn't be found, I'd be tempted to glue the caps in place w Seal-All or something --- not sure if that's a bad idea or not & wouldn't know until I tried it.

Side note: the caps seem like they would be a good candidate for 3D printing.

I was wondering this question myself a week or two ago so I searched the archives about it, Those plugs create a vacuum for that jet, My gaskets have shrunk and became hard so I ordered new ones (they aren't cheap from dealer) total came to about $45 for four little gaskets. They should be in today hopefully.
kzrider.com/forum/3-carburetor/316111-ke...4-carb-plastic-plugs

"Yes, you need those plastic plugs. BIke will run ike crap if they are missing - if it runs at all. The pilot jet gets its gas from off either the secondary or primary main through an internal passage. I remember putting O rings on the plugs but not having the problems you mentioned. I've heard others say they were a tight fir and they had to trim them. Perhaps I used the larger O rings. I know I did'nt put any on the drains ." -JR

Edit: Found something Patton has posted here that may shed more light on the topic
kzrider.com/forum/3-carburetor/379440-11...-no-longer-available

They just ensure the pilot jet is fed through the main jet instead of from the float bowl directly.

Your TK26 CV carbs have the plugs. In case anyone else is reading this, the ZX550 TK27 CV's don't have the plugs, even though the TK27 carbs are very similar to the TK26.

A small dab of silicone grease helps lubricate the O-rings and make them slip into the mating hole easier sometimes. As far as "carb kits" are concern, my view is to keep all the original brass parts like jets and just clean them with carb dip. I trust Mikuni/Keihin far more than aftermarket carb part makers, many of which have the parts made in China. Z1 Enterprises sell O-rings and gaskets for the carbs. 90% of the time that's all you need.