Air silencer cover for 1975 Johnson 115 V4

[Gilera]

My motor was missing the airbox cover when I got it.

Is it important to have this on for the engine to run properly or is it something people commonly remove? I have read that fuel will leak out of carbs when motor is tilted up if you don't have one on. I would have thought that it could affect jetting to remove it.

I am having a bit of trouble finding a replacement one locally in Australia. I can find one that is for a 1972 model (part number 0385254). Mine is listed as 0320048. It looks the same in the pictures except that it has removable grommets whereas I think the 1975 model didn't have these but could be wrong. The part number for the base is different between the two models too. Does anyone know if this earlier model cover will fit on my 1975 air box?