Trying to troubleshoot it. Up till this year it has been fine. Changed the 3 filters on the rotor end when it kept puffing black smoke. It ran better for a few weeks and now it wants to puff again. I run a small exhaust fan while the heater is on but when it puffs I shut it off and let it clear and take a break. Where is the fuel filter at? Also, should I invest in a gauge to check the air pressure coming out of the rotor? Where to buy one? Ebay? How about the photocell? Just clean it? 