What David C said.
: Plus the air intake on our 147 is open to atmosphere, under the vented plastic scuttle panel. If you look down the hole,there sits the axial fan, ready to collect leaves and debris.
: Adjacent to this hole are two vacant, (unused,) fixed, threaded studs. As I said in a much earlier post, I made a plastic frame up, held by nuts and washers, on these threads, that retains a Bounty kitchen roll towel, cut to size, this allow the air to pass unresticted, collecting dust, pollution, flies, leaves, in fact debris in general, long before it reaches the fan, or any other part of the system. Good modification, IMO.
: Has worked effectively for a while now, the Bounty towels do not tear, or disintegrate, even when wet.