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O.S. - OSMG1720 OSM13941 13941 531028021327 4531028021327
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O.S. 21XM VII Water Cooled Outboard Marine Engine
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O.S. 21XM VII Water Cooled Outboard Marine Engine
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Instruction Manuals: Manual 1 (3.4 MB)
Tower Catalog Page: 175

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Tech Notes
This is the O.S. 21XM Version II Air Cooled Outboard Marine Engine.

****** Because of the competition nature of this engine,******
******it is NOT covered by the O.S. 2 Year Warranty.******


Designed expressly for small and medium size outboard boats
Installed aluminum tilt transom mounting plate
Preassembled outboard unit with flexible propeller
Blue anodized aluminum heat sink head
42mm carbon fiber propeller
20J carburetor


O.S. 21XM Version II Outboard Marine Engine, Muffler, Mounting Plate,
#8 Glow Plug, Propeller, Outboard Unit, Steering Arm and


Glow Fuel: 10-30% nitromethane content, use 20% for break-in
Glow plug igniter and shore equipment


Displacement: .21 cu in (3.5cc)
Bore: 0.654" (16.6mm)
Stroke: 0.630" (16mm)
Practical RPM: 3,000 - 25,000
Power Output: 1.3 PS, 1.28 HP @ 25,000RPM
Weight: 24oz (682g)
Carburetor Settings:
Needle Valve; 2.5 turns from fully closed
Mixture Control Valve: Shoulder portion exactly at a tangent to
the throttle rotor hole
Distance between mounting hole centers same side: 0.98" (25mm)
Distance between mounting hole centers opposite side: 1.5" (37.5mm)
Distance/outer mounting hole centers on steering arm: 2.5" (64mm)
Width of muffler: 1.8" (46mm)
Distance from flywheel to skeg: 8.6" (219mm)
Distance from mounting plate bottom to skeg: 3.4" (86mm)
Distance from mounting plate top to flywheel: 3.5" (87mm)
Distance from mounting plate to end of cavitation plate: 7.2" (183mm)
Distance from mounting plate to prop attachment point: 5.9" (149.5mm)
Distance from bottom of mount to driveshaft center: 1.3" (34.5mm)
Height of mounting plate: 1.8" (46mm)


cone. Any attempt to start engine in a counter-clockwise rotation
may cause serious damage to the engine. Because of the clockwise
rotation, the crankshaft has reverse threads.

jxs 05/25/11

– If you need more information, use these O.S. resources –
Click Here: Manufacturer's Product Web Page
Email: enginesupport@hobbico.com
Web Site: http://www.osengines.com/
Phone: 217-398-8970
  Postal Address:

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Accessories Needed
This is the Air Cooled O.S. 21XM Outboard Marine Engine. FEATURES: Designed for small and medium size outboard boats, tilting transom motor mount, carbon fiber prop, muffler, blue aluminum heat sink head REQUIRES: Glow fuel with 10-30% nitro content, starter belt and shore equipment

Accessories for the O.S. 21XM VII Water Cooled Outboard Marine Engine

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