The air intake warning light (which I assume is supposed to mean that the filter is clogged or air intake is blocked) is gradually coming on around 2000 rpm, and reaching maximum brightness around 2400 rpm. I thought the filters were clean (less than 100 hours, and looked fine), but I changed both. The effect was minor, so I took out 1 of the 2 filters, and got about 300 rpm more before the warning light first appeared. The engine runs fine, and the exhaust is normal. I've never run the tractor (about 460 hours, usual servicing, no problems) without both filters, and the tube from the filter housing to the carb seems fine (at least as far as I can see). So, where's the problem (L3410)?