"Man what a bunch of diehard smarty's here. How could using the same material be skimping? And having it extend beyond the filter holding box. Paying $8 for a tiny 4-5" paper filter is too much, considering a giant paper home AC filter is a fraction of the cost, and made from the same material. My mower isn't worth $50 anyway. The filters are way overpriced on purpose and is just a way of raping you for more money. Just like $1 USB cables are jacked way up to $20-$30 when Best Buy, etc tries to sell you them along with your new printer. Guess I picked a bad place to ask. I've read online of people making their filters for other applications (automobiles, etc), but I guess no one here has heard of such a thing." When I look at the $8.00 OEM Briggs air filter I just purchased I'm struck by the following: 1. It uses a flexible plastic surround that secures the media and seals the air cleaner housing perfectly. I have no idea how you propose to create that part of the air filter assembly. It is vitally important that air go through and not around your home-brew air filter. 2. The filter media itself is deeply fluted and provides a large filtration area. Most home AC filters I've seen are not nearly as deeply fluted and would not be nearly as effective. If you want to jury-rig some home-made filter by cutting up an air conditioning air filter then I say go ahead. Most of use have lawn mowers that we paid well in excess of $50.00 for and intend to keep them running properly for a couple of decades or longer. Most of us have better things to do than spend the time creeating a homemade air filter when a reasonably priced well designed replacement is available.

Go to the Subaru-Robin page and look up service and support. They have both parts list and service manual for your EH18. The service manual has specific info about setting the governor. You can then pull down a PDF of the two manuals. See the link below. Here is a link that might be useful: Subaru Manuals

We see this problem all the time and more than likely your Return Duct leaking or sucking in the dust, since the supply air is blowing air OUT, your vents, and the return duct sucks in and I'd bet it's the area directly behind the filter grille. Is the wall cavity above and below the grille covered? also are the panning edges and headers sealed with caulk or tape? If they're taped, then that could be your problem, tape doesn't last like caulking.

There's no way for the thermostat to know that you've gone into your attic and changed a filter unless it operates off some sort of sensor as RyanHughes mentioned above. Assuming the indicator is a simple timer that counts the accumulated blower run-time ... you have to to press a button or something to reset/restart the timing when you change the filter. My thermostat, for example, has a designated button labeled "Reset Filter."