An airbox of some form will always run better than pod filters, no lid is the easy way, it's very noisy though, but some people like that.
I found mine runs better with the lid on and a couple of 1 1/2" holes in the lid.
Be carefull, on the 18 and 21 the lid is a large part of the restriction (it is on the '28 too but so are the exhausts), jet accordingly.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread