Mercury Carb Rebuild Question

Just finished rebuilding all three carbs on a '98 Mercury Factory Jet 60/45. The motor is actually a 60EO. The carbs have a threaded opening just to the left of the idle adjustment at top right.

There were no plugs in any of the carbs, but the rebuild kits contained threaded plugs that fit the openings perfectly. The opening enters into a small chamber on top of the carb. In this chamber there is an open passageway leading to the top of the float chamber and float bowl. It seems to me that an opening like this would be a good place for dirt and other foreign particles to get into the carbs. The carbs were pretty dirty inside the float bowl and one of the main fuel jets was almost completely stopped up. My question is this; anyone know if these carbs are actually designed like this or if there were plugs in the carbs at one time and they were removed for some reason?

Photo (not very good) of plug below.

Larry, I could be wrong but I think that hole accepts part #6247 Vent Jet .90-50/60. Looks like you have the part
https://www.boats.net/parts/search/Merc2/Mercury/60%20%283%20CYL.%29/0G290585%20THRU%200G589999/CARBURETOR/parts.html

You could be right about the hole being there for that jet, but the part I have is a plug. It doesn't have a center hole like a carb jet. That part isn't shown on the schematic for my motor so I guess they just left the hole open.

https://www.boats.net/parts/search/Merc2/Mercury/45%20JET/0G590000%20THRU%200G760299/Carburetor/parts.html

I just rebuilt the carbs on my 1994 60/45 Mercury jet and the kits had those plugs in it. My carbs have the 090 (or 060) jet in them so I cleaned them and put them back in. I was able to get in 1 last run after the rebuild to verify it was running correctly, I just had to make some idle adjustments (which are almost meaningless in cold weather since it will need to be readjusted once it gets warm).

From looking at the schematics, the '97 and older Jet 45's use different carbs than the '98 and newer. The older carbs have the 6247 vent jet and the newer ones don't use then, but still have the threaded hole for venting.