I popped the filter cover off my Honda mower, and while there is room to stuff a piece of foam on top of the paper filter, I don't see what good it would do considering there would be gaps between the two filters. Basically, nothing would force the air through the pre-filter. Decided to pass on that idea. While there, I vacuum out the stock filter and put it back. Even with a decently powerful shop vac, using a brush attachment, it wasn't putting undue stress on the filter media. And while on this subject, I hit Amazon for a spare filter, and found a set of four filters for the princely sum of $9. For something like this, I'd normally buy OEM, but these filters have 86% 5-star reviews, and only 1% one star (1186 total reviews). About as good as it gets.
