O.S. 21XR-B Version II Car Engine

Tower Stock# OSMG2056  •  Manufacturer Stock# 1AW00
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Notes from our tech department:
This is the 21XR-B Version II 1/8 scale Buggy Engine from O.S. Engines.


Ideal for up and coming 1/8 scale buggy racers and backyard bashers
Upgradeable with high performance O.S. Speed parts
Blue anodized aluminum cylinder head
Easy to tune 21J3-I slide valve carb with 7mm yellow restrictor for
more bottom end performance, and red 8mm restrictor for greater top
end speed
Natural finish crankcase


21XR-B Version II ABC Buggy Engine with Slide Valve Carb, 7mm & 8mm
Restrictors, P3 Turbo Glow Plug, Exhaust Seal Ring, two Dust Caps,
and Instruction Manual


Fuel: 10-30% nitro content, 20% recommended for break-in
Exhaust System: Depending on vehicle
Glow starter, fuel tubing and track equipment


Displacement: .213 cu in (3.49cc)
Output: 2.45 PS, 2.42 HP/33,000RPM
Practical RPM Range: 4,000 - 40,000
Bore: 0.641" (16.27mm)
Stroke: 0.661" (16.8mm)
Weight: 13.40oz (380g)
Crankshaft Size: UNF1/4-28
Distance Between Mounting Holes Same Side: 0.83" (21mm)
Distance Between Mounting Holes Opposite Side: 1.45" (37mm)
Height Bottom of Mounting Tabs/Top of Cylinder Head: 3.4" (86.5mm)
Width at Mounting Tabs: 1.8" (45mm)
Width of Crankcase below Mounting Tabs: 1.2" (31.6mm)
Distance from Backplate to Front Bearing: 2.5" (64.5mm)
Distance from Center of Crankshaft to Front Bearing: 1.7" (44mm)
Distance from Center of Crankshaft to Backplate: 0.81" (20.5mm)

Carburetor Settings, NOTE carburetor is preset at factory and
requires very small adjustments
Needle Valve: Run vehicle with throttle fully open a few times over
long straight course to observe vehicle speed. Close needle valve
15 and repeat run. Gradually close needle valve in subsequent
runs to achieve highest speed taking care not to close needle
valve too far and overheat engine.

Metering Needle: With engine running, close throttle and allow
engine to idle for about 5 seconds then fully reopen throttle.
Turn metering needle clockwise 15-30 to lean mixture if
excessive smoke is observed, or counterclockwise 15-30 to
richen mixture if engine speeds up momentarily and then cuts out

Throttle Stop Screw Adjustment: Turn counterclockwise to reduce
throttle opening if engine runs too fast with throttle closed.

jxs 09/04/17



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