This is the Magnum XL91 RFS Four-Stroke Aircraft Engine with Blue Rocker Cover. FEATURES: Aluminum piston, iron piston ring and steel cylinder sleeve for long life and high power output Dual ball bearing supported crankshaft and camshaft Dual needle valve carburetor insures precise fuel/airflow metering High-flow muffler One year limited warranty through manufacturer INCLUDES: Magnum XL91 RFS Four-Stroke Engine with Muffler, instruction manual and parts list REQUIRES: Fuel: For break-in, 10% 2-stroke airplane blend For normal use, 15% 4-stroke airplane blend Glow Plug: 4-stroke "hot" type Break-in Propeller: 14x6 Glow starter, fuel tubing and field equipment SPECS: Displacement: 0.91 cu in (15cc) Bore: 1.09" (27.7mm) Stroke: 0.97" (24.8mm) Crankshaft Diameter: 5/16" Practical RPM: 2,000 - 12,000 Weight with Muffler: 22.4 oz (635g) without Muffler: 20.7oz (587g) Distance Between Mounting Holes Same Side: 1.02" (26mm) Distance Between Mounting Holes Opposite Side: 2.04" (52mm) Width at Mounting Tabs: 2.4" (60mm) Height from Bottom of Mounting Tabs to Rocker Cover: 4" (101mm) Height from Bottom of Crankcase to Rocker Cover: 4.7" (120mm) Distance from Backplate to Front Bearing: 2.9" (74mm) Distance from Backplate to end of Crankshaft: 4.9" (125mm) High Speed Needle: Turn in completely then back out 2-1/2 turns Low Speed Needle: Do NOT adjust until engine is broken in. Hold carb barrel open, turn needle screw counter-clockwise until it stops then turn in clockwise 4-1/4 turns-this is the factory setting COMMENTS: Some Differences Between 4-Stroke and 2-Stroke Engines; 4-strokes are quieter. 4-strokes get better fuel economy. 2-strokes generate more RPM 4-strokes generate more torque and will swing a larger prop. 4-strokes have a realistic sound; like a real aircraft engine. jxs 7/02/09 ir/jxs