LRP electronic GmbH
Hanfwiesenstraße 15
73614 Schorndorf
Germany
MA00263 © LRP electronic GmbH 2016
USER GUIDE
2.82 PS
39.800 RPM
ZR.21X SPEC.3
DEAR CUSTOMER,
SPECIFICATION
FUEL
CARBURETOR
AIRFILTER
A good airfilter is very important for the life of your engine. Never run without an airfilter, as quick and permanent
damage will result! Don’t forget to impregnate the airfilter with a suitable oil before usage. Carefully clean the airfilter
at least after every tenth tank. Replace the airfilter every 3 litres (~1 gallon) of usage.
We recommend the use of our LRP Hi-Flow 2-Stage oval airfilter (No. 36565) together with our LRP Hi-Flow airfilter
oil (No. 36590).
Never use regular gasoline or airplane fuel. Use fresh 2-stroke model car fuel only! We recommend using our line of
LRP Energy Power fuels (No. 35711: 25% 1L / No. 35731: 25% 3,5L). For the LRP ZR.21X Spec.3 engine, we recom-
mend a fuel with 25% nitro. Never exceed 36% nitro. A higher nitro content will decrease your engine‘s lifetime.
thank you for your trust in this LRP product. By purchasing a LRP nitro engine, you have chosen a high-performance
and highly sophisticated product, which doesn´t make any compromise between maximum performance and easy
tuneability. We hope you enjoy your new engine.
Please read the following instructions carefully before you start using your LRP ZR.21X Spec.3 engine. This user guide
contains important notes for the installation, the safety, the use and the maintenance of this product. Thus protecting
yourself and avoid damages of the product.
Proceed according to the user guide in order to understand your LRP ZR.21X Spec.3 engine better. Please take your
time as you will have much more joy with your product if you know it exactly.
This user manual shall be kept in a safe place. If another customer is using this product, this manual has to be handed
out together with it.
Idle screw (#1):
Adjusts the air flow when carburetor is fully closed. Turn CW for higher idle-speed and CCW for lower idle-speed.
Should be open approx. 0.5mm.
Mid range needle (#2):
Adjusts the mid/low-speed flow rate of the fuel. Turn CW for leaner and CCW for richer setting.
Main speed needle (#3):
Adjusts the main flow rate of the fuel (when the throttle
is opened significantly). Turn CW for leaner and CCW for
richer setting.
Carburetor venturi inserts:
In order to affect the fuel/air mixture, you can use dif-
ferent venturi inserts on this carburetor. These are to
finetune your engine to different track layouts. There
are different venturis coming with the engine: 7.0mm
and 6.0mm.
- 7.0mm has the most power, 6.0mm has the best fuel
mileage.
Engine size
.21 (3.49ccm)
Bore
16.26mm
Stroke
16.80mm
Number of ports
5 + 3 (5 x transfer-, 3 x exhaust-port)
Main bearing
Standard
Crankshaft
14.0mm / precision balanced / with silicone insert
Crankcase
Black XTEC C6 .21 Heavy-Duty Competition
Piston
CNC machined / specially lightened / high-silicium alloy
Connecting rod
Oversized, flow-optimized milling, extra strong aluminium
Glow Plug
Hot Turbo style, LRP Turbo WT3 (No. 35135) included
Carburetor
XTEC thermal protected WorksTeam carburetor. Aluminium 6.0 and 7.0mm inserts included.
Power output*
2.82 HP
Max. RPM*
39.800 RPM
Suitable for
1/8th Offroad Buggies and Truggies for competition use
*figures may vary depending on used fuel, muffler and tuning.
GLOWPLUG
Use only Turbo style glow-plugs (also known as conical style plugs) for this engine. We recommend using our line of
high-quality LRP Platinum / Iridium WorksTeam glowplugs (No. 35135 - No. 35145, availabe as WT3 and WT4). Check
them frequently and never run with worn-out or old glow-plugs since they could damage your engine. They turn dull
when your engine was too lean and should be replaced. They should stay bright like chrome. If the glowplugs wear out
too fast, an additional 0.1mm shim between burnroom and liner is recommended. Whenever you have trouble with the
engine stalling for no reason, replace the glow-plug first!
TIP: Our LRP team always uses a LRP Platinum / Iridium WorksTeam WT3 (No. 35135) plug for the LRP ZR.21X
Spec.3 engine.
EXHAUST SYSTEM
Never run without a pipe since this will cause excessive overheating and may damage your engine. A good pipe has a
very huge effect on the performance of a 2-stroke engine. For the LRP ZR.21X Spec.3 engine, we recommend using our
high-quality LRP Screamer-93 1/8 Off-Road Exhaust System (No. 36255) for maximum performance.
HEAD CLEARANCE
We recommend a real head clearance between piston and burnroom of about 0.60-0.70mm (0.024-0.027“) or more,
when the piston is at Top Dead Center. The real head clearance can be calculated as follows:
Real head clearance = Thickness of head shims + 0.25mm*
We suggest to start with 0.40mm (0.016“) shims underneath the combustion chamber. You may want to adjust the
shims depending on nitro-content (see table) or track layout. Large tracks may require an extra 0.10mm (0.004“) shim
to reach higher topspeed and improved fuel consumption, but this will decrease acceleration slightly.
Nitro content
16%
20%
25%
36%
Real head clearance 0.65mm / 0.025“
0.65mm / 0.025“
0.65mm / 0.025“
0.75mm / 0.029“
Head shims
0.40mm (0.016“)
0.40mm (0.016“)
0.40mm (0.016“)
0.75mm / 0.029“
* (that‘s due to the internal construction of the engine and the compression of the head shims, when the cooling
head is mounted)
RUN-IN
Proper run-in of the engine is a very important step in ensuring that you get the highest performance and lifetime of
your engine. Take your time for proper run-in.
Do not use run-in benches, but use your car for run-in.
Use the same
fuel as you will be using for the life of the engine. Special run-in fuel is not needed. If your engine doesn’t start easily
you may try loosen the glowplug by ½-turn to decompress the engine and try again. Don’t forget to tighten the glow-
plug again once the engine started!
Procedure:
• Start the engine and set the main-needle very rich, i.e. excessive smoke coming from the muffler. The factory set-
tings are a good starting point.
• Let the engine idle for 2mins first to warm it up.
• Now start driving your car, it will be slow and sluggish, but this is an important step.
• Do not allow the engine to rev-up too high, run the engine at half speed on the straightaway.
• The engine should not be too cold and not too hot during run-in, 70-80°C (160-180°F) is perfect.
• Let the engine cool down for 15mins after each tank during the run-in period.
• We recommend doing so for 10 tanks of fuel before you start tuning your engine.
TUNING
It never hurts to have the mixture too rich, but NEVER let the mixture get too lean. Always tune from rich to lean. If in
doubt, richen it up first! Never try to tune a cold engine, run 2-3 minutes to get the engine up to running temperature
before doing any adjustments!
Basic tuning procedure is as follows:
1. Set the engine’s idle speed up slightly higher than normal.
2. Start tuning your engine with the settings too rich.
3. Always tune main-speed needle (top-end) first.
4. Tune mid-range needle next.
5. Reset idle speed screw.
Procedure:
1. Set the idle speed so your engine doesn’t stall (slightly higher then normal).
2. Go to the track with the main-needle set too rich, there should be heavy smoke coming from the muffler now.
3. Tune the engine by leaning the main-needle 1/8 turn at a time (turn clockwise).
- Your goal will be that the engine will just reach maximum RPM on the straightaway.
- Open the main-needle again by an 1/8 turn (turn counter-clockwise) when you have reached that point. This
should be the perfect setting for the main-needle. Temperature of 95-105°C (200-225°F).
- If the main-needle is set too lean, the engine will overheat and will not accelerate smoothly.
If this happens, immediately stop the engine and richen the main-needle (counterclockwise) 1/4 turn before a new
attempt.
4. Adjust the mid-range needle now. Run 3 full laps, stop the car near you and let it idle for 5secs. „Push off“. It should
have slightly richened up (idle rpm gets lower), but still accelerate quickly. If it died before the 5secs, check the
following:
- If the rpm constantly decreases and finally the engine stops, the mid-range needle is too rich.
- If the idle-speed increases during idle, the mid-range needle is too lean.
5. You may have to re-adjust the idle-speed now. If it idles too high, the clutch may not release completely and you
will lose „snap“ off the corners. If it idles too low, it may stall at the start, or at the end of the straightaway when you
release the throttle.
Ways to measure the engine temperature:
• Temperature gauge method (recommended): Pull in quickly and immediately take a temperature reading. Place the
gauge directly over the engine pointed at the glow plug.
• Spit method: Pull in quickly and immediately put some spit on the engine’s head. The spittle should just slowly boil
off (2-3secs). It should not dance around as if it were on a hot griddle, nor should it lay there and steam.
BEST-NR. 32112
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