I have an American Standard Freedom 80 LP furnace. When it tries to fire the bottom burner will not always light, so it shuts down and tries again. Most of the time it will light on the second try, but sometimes it times out after the third try. I have removed the burners and have clean them with a thin knife. I have removed the orifices and made sure they were clean. I finally hooked up a manometer and got 9.5 to 10"WC inlet pressure. The manifold pressure is the same. The furnace calls for 11"WC. Obviously I can't adjust the regulator to get a higher manifold pressure.Would the lower pressure cause my furnace not to light properly? What should my LP inlet pressure be?