Needing some guidance on a backfire issue. 1993 omc king cobra 7.4 liter. Sit for 5 years. Boat was winterized. 2 weeks ago we tried getting it going. Drained all fuel (7 gallons) put new fuel in, rebuilt carb holley 4150. New plugs,wires,cap and rotor. Checked compression 6 of cylinders 151lbs...
