Starting & Tuning the Traxxas TRX Racing Engine™
feature will be useful for anyone who has just purchased a new Traxxas
nitro powered vehicle and also those of you who are looking into
getting one of your own. It will cover initial setup, as well as in
depth tuning instruction. Some of the tips may even be helpful to some
of you nitro veterans out there as well, so grab your gear and let's
Tools and Accessories:
article will show how to tune a T-Maxx 2.5, but the same procedure can
be used for any 2.5, or 3.3 engine. As with all Traxxas RTR vehicles
the T-Maxx comes pre-assembled with radio gear already installed. The
instruction packet included in the box contains some important tools
and accessories that can be used to perform minor maintenance tasks and
repairs. Basic hand tools such as screwdrivers, pliers, wire cutters,
etc. will be necessary to perform major disassembly of the truck. There
will also be some accessory items needed to keep your truck up and
running. I'll run down a list of important and handy items that will
make working on and tuning your new Maxx a much more pleasurable
experience. Some of the tools listed below are not absolutely necessary
but will make tuning quicker and easier. I've listed only the tools
that would be useful for this particular segment. There are other items
that will be handy for future articles on tuning and maintaining the
1. Small flat tip model engine-tuning screwdriver
2. #1 Phillips screwdriver
3. Medium size wire cutters
4. Medium size needle nose pliers
1. Spare glow plugs (#3231, #3232, or #3232X)
2. CA glue (for tires)
3. Fuel 10%- 33% (Traxxas Top Fuel™ recommended)
4. Fuel bottle
/ Radio System Pre-Check:After pulling your vehicle out of the box and
reading through the instructions it's a good thing to run a quick
check over the chassis and radio gear to make sure that everything is
functional and in order. You all do read the instructions don't you?
You know the book with all of the pretty pictures and diagrams in it? I
thoroughly recommend reading it carefully.
It's packed with some very important and interesting stuff. The T-Maxx
instruction manual is the best manual that I have personally ever read
in an RC vehicle kit. If you follow the directions that are written in
its pages, it might just be the difference between having countless
hours of fun with your new monster truck or pulling your hair out one
strand at a time. Nobody really likes the latter, no matter what they
tell you, so let's read the manual.
After gluing the tires and
installing the radio system batteries, the next step is to perform a
radio systems check. Checking the radio system is the first thing that
I'll cover and is probably the most important. A malfunctioning radio
system can potentially cause more damage than any other component on
the vehicle due to a runaway crash. It is very important to perform a
radio system check every time that you plan on running the truck. Make
sure that all three servos have full range of motion and are not
glitching or binding in any manner.
that the front of the truck should be lifted up to get full steering
range due to the zero-scrub steering design. This design utilizes the
centrifugal force of the wheels to help steer the truck. When the truck
is rolling the steering has no problem going from lock to lock.
make sure that the slide valve in the carburetor is returning all the
way back to the preset idle position and that it is operating smoothly.
checking the servo functions, perform a range check with a friend.Make
sure that there are new batteries in the radio system and that the
antenna mast is fully extended. Turn both the truck and the transmitter
switches on. Now, have a friend walk away with either the truck or the
transmitter to the farthest distance that you plan on operating the
truck and operate all radio functions. All three channels should work
fine. If there is a range problem or the system is glitching do not
proceed to operate the truck until the problem is diagnosed and
There are many things that can cause radio
interference outdoors like power lines, large outdoor antennas and CB
radios. If you are trying to run indoors things such as metal beams,
fluorescent lamps and computer monitors can cause interference. Before
you think that the radio system is faulty, try another location and see
if the problem clears up.
After checking the radio
system functions there are a few things to check over before firing up
the engine for break-in. ere's a quick checklist:
sure that there is a zip-tie around the base of the airfilter. This
will keep the airfilter secured to the carburetor. It is very important
that the airfilter stays on the carburetor anytime that the engine is
running. Running the engine without an airfilter can and will cause
severe damage to the piston and sleeve ruining the performance of the
last thing that we'll check before heading out to break-in the engine
is the seal between the fuel cap and the tank. This is adjustable with a
2.5 hex wrench. Your lid may not need adjustment, but it's a good
thing to check anyway. The orange o-ring that seals the tank should fit
snugly into the filler neck of the tank.
It should also fit
all the way down into the filler neck.If the cap closes very easily
with out any tension between the o-ring and the filler neck, then the
o-ring is set too loose. Turn the adjustment screw clock-wise to
tighten. This will spread out the o-ring providing a tighter fit. The
opposite is needed if the cap will not retract all the way back into
the filler neck.
Break-in Tips and Settings:
that you have checked over your T-Maxx and everything is ready to go
it's time to break-in the engine. I'll go over a few common problems
that may occur and how to fix them, and possibly avoid them in the
Factoy break-in (default) carburetor settings:
A good starting point for the TRX 2.5 or 3.3 hi-speed needle is 4 turns out (counter-clockwise) from closed.
the thin darker gray area between the low speed needle and the
throttle arm. This is actually the other end of the slide valve from
inside the carburetor. The low-speed needle is threaded into the slide
valve and is set flush (even) with the edge of the slide valve.
(Roughly 1.5-1.75 turns from closed) Note: This is a good base setting.
Adjustments may need to be made to the low-speed needle for best
performance in your running conditions.|
The idle stop screw controls the idle speed by preventing the
carburetor slide from closing completely. Turn right (clockwise) to
increase idle, and left (counter-clockwise) to decrease idle.
A good starting point for the slide valve to stop at idle is a 0.7mm-1.0mm gap.
carburetor is preset at the factory for break-in. The base setting
should be right to start and run the engine through the break-in
process. However, if you are having trouble getting the engine started
or keeping it running, then you may need to readjust the fuel mixture
to compensate for factors such as temperature, humidity, and altitude
(air density). It is a good idea to bring the little tuning card that
was attached to the fuel tank with you.
is a very informative card and will be extremely valuable, especially
to those of you that are new to nitro RC. You can tear the card at the
perforation and place it in your wallet or pit box. I wish that I had
one of these when I got into nitro many years ago. It would've saved me
from many hours of frustration.
Starting the Engine - After
filling the tank with fuel, install a freshly charged battery into the
EZ-Start® 2 control box. Turn the transmitter and the truck on. Plug the
EZ-Start® controller into the receptacle located in the middle of the
rear body mount. Note that the controller will only key into the
receptacle one way. Do not immediately prime the engine. Priming the
engine is only necessary if the fuel is not making its way to the
carburetor. Press the red button on the controller. This will spin the
engine over while heating the glow plug at the same time. Note that
both LED lights on the EZ-Start® controller should be lit green. If
either light is not lit then there is a problem with that function.
EZ-Start® should turn the engine over at a sufficient enough rate to
draw the fuel into the carburetor within a reasonable amount of time.
Look at the fuel line and watch the fuel make its way up to the
carburetor. To help speed up the fuel to the carburetor you can prime
the engine by placing your finger over the outlet of the exhaust pipe
for just a brief second or two. You can see the fuel work its way to the
carburetor very rapidly. Caution: Priming the engine for too long will
then flood the engine causing it to hydro-lock. Fortunately, the
EZ-Start® 2 system was designed with thermal protection and overload
cutoff circuitry. This feature will keep the EZ-Start® motor from over
There are two ways to lock an engine during start-up:
Engine flooded - Too much unburned fuel in the engine crankcase will
cause the engine to hydro- lock. A rich hi-speed needle setting or
priming the engine for too long during start-up usually causes this.
Also, a fouled glow plug can cause the engine to flood by not heating
up to burn the fuel. Keep your eye on the glow plug LED on the
controller. This light will tell you if the plug is not heating up.
Read on for clearing a flooded engine.
Piston stuck at TDC (Top Dead Center) - A brand new engine will
typically have a tight fit between the piston and the top of the
sleeve. The sleeve has a tapered fit to the piston. The fit should not
always be too tight to start the engine, however a weak starter battery
or one that has not been charged fully may not deliver enough power to
crank the engine over at the appropriate RPM to keep the piston from
Make sure that you are using a good quality battery
pack that is fully charged. This is especially important with a new
engine that needs to be broken-in. If you've tried starting it for
several minutes now, try a quick recharge on the starter battery for a
little extra voltage. If the engine is stuck at TDC, then use a flat
blade screwdriver to rotate the flywheel over. Place the blade into one
of the grooves of the flywheel and push down turning the flywheel
counter-clockwise when viewed from the front.
You should see the flywheel turn and you should feel the piston become
unstuck from the sleeve. Before trying to restart the engine replace
the starter battery with a freshly charged pack or a freshly charged
battery pack of better quality.
If the button is pressed too
long after the engine stops turning over, the controller will stop
sending power to the electric motor. When this happens the motor LED on
the controller will not light. This means that the thermal cutoff
circuitry was tripped inside of the controller. Allow the EZ-Start®
controller to cool for 5 to 10 minutes before trying to start the
engine again. If the engine sticks at TDC, use the procedure above to
free it. If the engine floods, then follow the steps below to clear it.
Clearing a Flooded Engine - Clearing a flooded engine is an easy process.
Disconnect the blue glow plug wire from the glow plug and take the
glow plug out of the engine with the two-way glow plug wrench included
in the instruction bag. Disconnect the fuel tubing from the carburetor
and plug the fuel tubing with a clean 3mm machine screw. This will keep
fuel from running out of the fuel tank and making a mess. If the fuel
tubing is not disconnected, then more fuel can make its way into the
engine defeating the whole purpose of this procedure.
Plug in the EZ-Start® 2 controller, tip the truck over on its side and
press the red controller button for about 8 to 10 seconds. This should
turn the engine over at a very rapid rate spitting out all of the
excess raw fuel from the crankcase and combustion chamber of the
engine. If there is still fuel coming out of the engine after a 10
second burst then release the button for a few seconds and repeat
another 8 to 10 second burst. Repeat this process until all fuel has
exited the crankcase.
3) Wipe up the raw fuel
from the cooling head with a paper towel and reinstall the glow plug
back into the head. Make sure that the little copper glow plug gasket
is located correctly onto the glow plug before installation. There is a
tapered edge between the threads of the plug and the hex body of the
plug. This should match up with the tapered (concave) side of the
4) Reconnect the blue glow plug wire and
place back into the protective slot in the head protector. To get the
blue wire back onto the plug securely, it helps to use a pair of needle
nose pliers to press the connector down over the plug. Take out the
screw that was used to plug the fuel line and reconnect the fuel line
to the carburetor. Your engine is now ready to start. Do not try to
prime an engine that was just cleared out. There should be plenty of
fuel residue inside the engine to start-up. The engine should fire up
Once the engine is started it
will act a little sluggish and boggy at first. Accelerate to roughly
1/4 throttle rpm or as necessary to get the vehicle to start moving. Go
ahead and drive the truck slowly back and forth to make sure that the
truck is tracking straight and that the engine is idling down when you
let off of the throttle. If everything is in order then carry on with
the break-in procedures.
If the truck is not tracking straight
and the steering trim on the transmitter is not correcting the matter,
then try adding a little bit of toe-in to the front and/or the rear of
the truck. Making the turnbuckle links a little longer will increase
will give the truck more stability. If the engine seems very sluggish
and wants to stall when you let off of the trigger, it may be normal.
If this tendency is very common during your first few tanks, then the
engine is probably set a little too rich. Try leaning out on the
hi-speed needle 1/16 of a turn until it stays running. Keep inmind that
the engine will provide strong performance even at a rich break-in
setting, so don't get carried away with mixture adjustments at this
Follow the break-in procedure as outlined by the manual
and you will be rewarded with a faster and longer lasting engine to
show for it. If the engine is idling at a high RPM or is accelerating
extremely fast, then the mixture is too lean for your driving
conditions. Richen the hi-speed needle 1/8 turn until it idles down
immediately and is spitting a little bit of raw fuel out of the exhaust
After completing a few tanks of break-in you may
encounter a situation where the engine will have a hard time starting
or will want to die shortly after it is started. This is typically
caused by a fouled glow plug and is common while breaking in a new
engine. There are tiny particles that pass through the combustion
chamber during the break-in process that come from all of the new
components wearing in together for the first time. These particles can
foul the glow plug.
Replacing the glow plug with a new one will
bring the engine back to life. I get a lot of questions about which
plug to use in the new engine. I recommend using the #3231 heady duty
Traxxas plug exclusively with the new TRX2.5 engine. The #3231 plug has
a thicker element that will stand up to the extremities of the new
engine. The #3230 plug should be reserved for situation where a hotter
plug is needed, such as running in cold weather conditions. TRX 3.3
Racing engines run great on 3232 or 3232X glow plugs.
Be sure to
complete the break-in process before tuning the engine in for
performance. Once the fifth tank is completed, bring the truck in, and
shut the engine off to allow the engine to cool. Give the truck a quick
check over. If the engine ran fine through the full five tanks of
break-in, then I like to go ahead and change out the glow plug with a
new one at this point. Give the truck a good look over for loose screws
and make sure that everything is still in order as mentioned in the
Tuning the TRX 2.5 or 3.3 for Performance:
Hi-speed needle adjustment -
After running the truck through the five tanks of break-in it is time
to tune the engine for performance. The engine produces a lot of power
even at a break-in setting, but that's just the beginning. Start the
truck up and make a few passes back and forth gradually giving the truck
more throttle. Once you've made four or five passes back and forth,
the engine should be up to a good tuning temperature, (I'll speak more
on engine temperature later in this segment). Lean the hi-speed needle
by turning the needle clockwise 1/16 of a turn and make a few more
should increase the power output of the engine. The engine should
accelerate very quickly and rev up to a high RPM without cutting out or
running erratically. Remember, more lean doesn't always mean more
power. Tune the needle until you reach peak performance.
you let off of the throttle, the engine should slow down to a
reasonable idle without jerking the transmission into gear. Also, the
engine's RPM should not jump up and down when sitting at idle. The
engine should idle smoothly without engaging the transmission and
If you feel that the engine has not yet reached
its best performance, continue to lean the hi-speed needle 1/16 of a
turn at a time and make a few more passes. You must make a few
high-speed passes after each needle adjustment to determine what the
engine is going to do. As you lean out the mixture setting, the engine
may want to idle at a higher RPM. If this happens decrease the engine's
idle by turning the idle stop screw counter-clockwise until the idle
comes down to a reasonable level as described above.
that you should always see a puff of smoke from the exhaust pipe under
acceleration. As the truck builds speed the trail of smoke will become
less noticeable, but should always be there. If the smoke is gone, then
that means that there is an inadequate amount of lubrication going
through the engine and this can cause permanent damage to the piston
and sleeve. If this happens, richen the hi-speed needle ¼ turn until
you see smoke during your high-speed passes and the engine should get
back to running and idling reliably.
If you have found yourself
turning the hi-speed needle every which way and have lost track of the
setting and you are having no luck with getting proper performance,
take a deep breath and relax. Shut off the engine and think of a happy
place. Don't feel bad. Believe me, we've all done it at one time or
another. Turn the hi-speed needle all the way in just until it stops.
the needle out four complete turns. This is a good starting point for
break-in, which will put you back to where it was when you pulled it
out of the box. The base setting for the low-speed needle is when the
adjustment head of the needle is set flush with the metal housing that
surrounds it. Always start rich and tune for performance.
Low-speed needle adjustment - Once maximum performance is attained out of the hi-speed needle adjustment, it is time to adjust the low-speed needle.
is imporant to adjust the hi-speed needle first, before adjusting the
low-speed needle. With the hi-speed mixture set correctly, and the
engine producing good power and speed, bring the truck in and listen to
the engine idle down. If the engine is "hanging up" or taking a while
to idle down to a reasonable RPM, then the low-speed needle could be
Remember to try and get the idle down by adjusting
the idle stop screw counter-clockwise first. If the low-speed needle is
too lean, then the idle adjustment will not have much of an effect on
the idle. Turn the low-speed needle adjustment counter-clockwise a
little at a time until the engine RPM is comes down to a reasonable
The idle of the engine is affected by both of the needle
adjustments and the idle stop screw. The low-speed needle has a greater
effect on the idle speed than the hi-speed needle. One of the more
common problems that I see with tuning engines is that some people will
try and compensate for a low idle caused by rich low-speed mixture
setting by cranking up the idle stop screw.
Try to keep the
idle gap as small as possible. The gap is usually happy around the 0.7mm
to 1.0mm mark. If you find yourself having to go beyond the 1.0mm mark
then there is a good chance that the low-speed mixture is a little on
the rich side. If you are turning the idle stop screw out so much that
the RPM is no longer being affected but is still too high, then the
low-speed needle is too lean.
Keep in mind that the above
conditions and adjustments are usually found in an extreme situation
when the truck wants to kick into gear or the engine is hanging up
badly. Once you have corrected these problems or if they just simply do
not apply, then it's time to move on to fine tuning the low-speed
needle with the low-speed mixture test.
Before you proceed any
further, think about what your truck is doing. If you are already
getting excellent power and punch out of your TRX 2.5 and the idle is
smooth and consistent, then you need not adjust anything. Go have fun.
Try not to make a huge deal out of getting that "perfect" setting. The
TRX 2.5 produces so much power that it is not as critical to get that
"perfect" mixture to have a lot of fun with this truck.
test - Once the engine is up to a good running temperature, make a few
high-speed passes back and forth and bring the truck in. As soon as
the engine idles down pinch the fuel line between the EZ-Start® motor
and the carburetor with a pair of needle nose pliers. This will keep
you from burning your fingers on the cooling head. The engine should
idle up for 3 to 5 seconds then try to stall. Let go of the fuel line
just before the engine stalls. If your engine falls within the 3 to 5
second range then it should be good to go.
If the engine immediately stalls, then the low-speed mixture is too lean.
the low-speed needle counter-clockwise 1/8 turn and retest after
making a few more hi-speed passes. If the engine idles up for more than
5 seconds then lean the low-speed needle clockwise 1/16 turn and
Tuning the Engine in by Temperature:
the engine by temperature is another way to adjust the carburetor to
maximize performance. This is something that should only be used as a
guideline and should not be used as the sole tuning method. There
really isn't a perfect set temperature for every engine since these are
air cooled engines. Weather conditions, fuel type, ventilation and
many other variations around the engine will change the "happy"
temperature for each engine. I try to discourage nitro owners from
falling into this temperature trap.
The best way to
tune the engine is to watch and listen to what the engine is doing.
When the engine is running strong and reliably with plenty of smoke
coming out of the pipe, then check the temperature at that point. This
should be a guide to where the temperature needs to be for that
particular driving condition. Maximum temp for any condition should
generally not exceed 270 F, but some conditions or high revving race
operation may require warmer operating temperatures.
temperature can provide good feedback to make sure that you are going
in the right direction. If the temperature goes up but performance
doesn't increase, then the engine may be too lean. One way to bring
engine temperatures down is to cut a hole in the windshield directly in
front of the engine for extra airflow around the cooling fins. The hole
should be around 2" to 2.5" in diameter. This is definitely
recommended for anyone running his or her truck in a hot climate.
you follow these simple yet effective steps for tuning your new
Traxxas Racing Engine, I can assure you that you will have many, any
hours of high performance fun with your new Traxxas vehicle. The power
of this revolutionary small block engine is incredible. With the right
tuning skills the TRX 2.5 or 3.3 can offer unbeatable performance and
reliability whether you are out at the local track or in your own back