can anyone shed any light on the "air box mod". i have already done the gearbox and pgm mods on my 21 and have some swarbrick cans on the way, but what is this other mod.

I have seen three different mods done to the 21`s. One is to drill four 3/4" on each side of the airbox lid. I have also seen the entire air -horn inlets cut out. The most popular is to run a K&N filter for the stock airbox and omit the airbox lid and cable-tie the filter in place. I hope that helps.
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Mike

You can also remove the internal web, effectively doubling the size of airbox for each carb. Leave a bridge for the filter to rest on, but remove all of the lid web.
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