Many moons ago when I used an MC18 almost everyday I did the very same. We found that 4x 25mm holes worked best in the air box lid. However on long trips back in winter late at night I used to tape two holes up. Andy used to take the piss about having a night time setting.

Tank tape used to be able to be reused many times. Myself and Andy often used to stop half way home and pull the tanks off. Those where the days when neither of us used to leave the house without a jet kit.
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If I have to take the carbs off once more...