I have a DeWalt DXH190HD torpedo heater that I can not get to burn correctly. It burns fine with the cover off, but when I put the cover back on, it “surges”. The flame goes out and back on. If I restrict the air on the back of the heater, it runs slightly better. My air pressure is close to correct. (My gauge is bouncy). I’m thinking that I must not be getting enough fuel or too much air. I can’t turn down the air. The fuel filter is clean, I have replaced all the air and fuel lines, and cleaned the nozzle. The pump is clean and the veins move freely as they should. I have two other heaters that I have worked on and I got them to run good but this thing has got me pulling out my hair! Any ideas would be appreciated.