How much do the foam airbox vents for you airbox lid, help the performance of your quad? Do you need to rejet?

 

I've never used those little vents, but any time you increase the air flow to any degree you must also increase the fuel flow correspondingly; in other words, re-jet.I run a Moto Force vented, transparent lid, which required a one size fatter main jet.I'd think that the foam filters would work okay as long as the maintance was done often. If not, then the foam would not pass air & be worthless. On the Moto Force, the longitudinal slots are placed along the side of the lid keeping water entry to a minimum.