This is the O.S. 21XZ-M 3.5cc Inboard Marine Engine. ****** Because of the competition nature of this engine,****** ******it is NOT covered by the O.S. 2 Year Warranty.****** FEATURES: Designed expressly for 21 class boat racing 21D big bore carburetor allows use of high nitro fuel Blue anodized water cooled head INCLUDES: O.S. 21XZ-M 3.5cc Marine Engine with 0.2mm Head Gasket, Silicone Exhaust Seal, RP7 Turbo Glow Plug, two Dust Caps and Instructions REQUIRES: Glow Fuel: Boat blend with 10-30% nitromethane content, use 20% for break-in Exhaust system depending on boat Glow plug igniter SPECS: Displacement: .21 cu in (3.5cc) Bore: 0.640" (16.27mm) Stroke: 0.661" (16.8mm) Practical RPM: 4,000 - 45,000 Power Output: 2.75 PS, 2.71 HP @ 33,000RPM Crankshaft Size: 1/4-28 Carburetor Settings: Needle Valve; 1.5 turns from fully closed Mixture Control Valve: Turn clockwise 10° to lean mixture or counterclockwise to richen mixture, adjust in steps of no more than 45-90° Distance between mounting hole centers same side: 0.83" (21mm) Distance between mounting hole centers opposite side: 1.4" (37mm) Distance/mounting tab to center of exhaust: 1.1" (28.5mm) Distance/mounting tab to center of cooling inlet: 2.2" (55.6mm) Distance from exhaust center to mounting flange bottom: 1.1" (28.5mm) Width not including mounting flanges: 1.2" (31.6mm) Width including mounting flanges: 1.8" (45mm) Height bottom of crankcase to top of intake: Height bottom of mounting flanges to top of intake: 2.6" (66.1mm) Length from backplate to end of crankshaft: 3.4" (86.5mm) Length from backplate to front bearing: 2.5" (64.5mm) Length from crankcase center to front bearing: 1.7" (44mm) jxs 05/24/11 ir/jxs