engine roughness

[big al 08]

sometimes when the pressures are correct and it still runs rough, look for leaks, these planes are old and a lot of "o" rings are getting very hard and loosing sealing abliity, sucking air can show up as fuel stains. at higher settings an abundance of fuel is flowing into the system thereby making the leak/sucking air of little consquence. however at reduced power settings they can make a substanial impact as the quanity of fuel flowing in the system as it is much lower allowing the leaks/air sucking to super lean or starve it till it quits