I have recurring nightmares about the airducts, filters and other debri being sucked into the motor, and I have seen a few motors where this has happened. So I went to my local plumbing supplies and bought a couple of 90mm overflow vents for a rain water tank and then modified and fitted them as per the photos. It's not proven yet as it may impact on the volumetric efficiency, but they are fuel resistant and to some extent heat resistant. I'm also going to do a set for the ST4 and maybe the 999. Like I said, not proven yet.....