User Manual
Tuning the High-Speed Needle
To obtain the correct high-speed needle setting, start
the engine and drive your vehicle around for a minute
or two, applying full throttle frequently. Place a drop
of water on the cylinder head. If the water sizzles away
(evaporates immediately), the needle setting is too
lean. A correct needle setting will result in the water
evaporating after 3-5 seconds. If the water does not
evaporate, chances are good that the needle setting is
too rich. Lean the needle 1/16 of a turn and run the
engine again, adjusting the needle setting to get the
desired evaporation time.
Check the temperature each time you change
the needle mixture. Do not let the engine
overheat, as this will damage the engine.
Tuning the Low-Speed Needle
The low-speed needle (also referred to as the idle
mixture or idle needle) should be set after you’re
satisfied with the high-speed needle setting. After
achieving the proper operating temperature, reduce the
engine throttle to idle and pinch the fuel line with your
fingers close to the carb fuel inlet nipple. If the engine
dies immediately, the low-speed needle is set too lean.
If the rpm’s increase dramatically, the setting is too rich.
The ideal setting results in the rpm’s increasing just a
slight amount after pinching the fuel line.
Carburetor Restrictors
The DPS
™
21 engine features a slide-valve carburetor
and includes two inserts of various diameters. These
carburetor inserts are used to alter the power curve
of the engine. The two diameters included have the
following effect:
7.5mm
Develops good mid-range power; easier to control
than the 8mm insert; best for low to medium traction,
average-sized tracks/areas.
8.0mm
Maximum power for high traction, medium-to large-
size tracks; slight decrease in fuel mileage over the
7.5mm insert.
Engine Maintenance
Periodic maintenance must be performed in order
to keep your engine in proper operating condition. After
each day of running, it’s critical to use high-quality
after-run oil to protect the internals of the engine and
help prevent corrosion. The methanol used in the fuel
attracts moisture that can cause corrosion (particularly
in the ball bearings). Follow these steps after running
your engine:
1) Empty all fuel from the tank and fuel lines.
2) Remove the glow plug and air filter and add
5 to 6 drops of a quality after-run oil into the
carburetor and cylinder head openings. Turn
the engine over a few times to distribute the oil
throughout the engine.
3) Clean and inspect the engine, air cleaner and
fuel system.
Troubleshooting Guide
Problem
Engine won’t start
Engine starts, then dies
Engine starts and runs
for 1⁄2 tank, then quits
Tuning the Mid-Range Needle
The mid-range adjustment screw adjusts the
air/fuel mixture at half throttle and can dramatically
effect mid-range throttle response. For best results,
start with adjustment screw flush with the face of the
carburetor. This setting will provide a slightly rich
mid-range fuel mixture. For a crisper leaner mid-range,
desirable on high-traction tracks where maximum
acceleration is needed, turn the mid-range screw out
(counterclockwise) 1 full turn. To soften the mid-range
response (richer), turn the mid-range screw clockwise 1
full turn for a softer feel during acceleration, best suited
for low traction conditions.
Note: The mid-range adjustment screw and
low-speed needle work in unison. Any time
the mid-range adjustment screw is adjusted
it will be necessary to readjust the low-speed
needle. When turning the mid-range screw
in, the low-speed needle will need to be
backed out. When the mid-range screw is
backed out, the low-speed needle will need to
be adjusted inward.
Idle Stop Adjustment
The last setting to be made is the idle stop screw.
Turning this screw clockwise increases the idle speed,
whereas turning the screw counterclockwise will
make the engine idle at a lower speed. Ideally, the
engine should idle just fast enough to be reliable in
acceleration and transition from idle to full speed.
Avoid an idle speed that is too fast, as it will cause
damage to your clutch.
Possible Cause/Solution
plug
charged
disconnected
lean
speed set too low
(too lean)
settings