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Starting & Tuning the TRX 2.5 or 3.3 Racing Engine™ by Steve Slayden
This 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 get started.
Tools and Accessories:
This 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 truck.
Tools
1. Small flat tip model engine-tuning screwdriver
2. #1 Phillips screwdriver
3. Medium size wire cutters
4. Medium size needle nose pliers
Accessories
1. Spare glow plugs (#3231, #3232, or #3232X)
2. CA glue (for tires)
3. Fuel 10%- 33% (Traxxas Top Fuel™ recommended)
4. Fuel bottle
Chassis / 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-Maxxinstruction manual is the best manual that I have personally ever read in an RCvehicle kit. If you follow the directions that are written in its pages, itmight just be the difference between having countless hours of fun with yournew monster truck or pulling your hair out one strand at a time. Nobody reallylikes 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 nextstep is to perform a radio systems check. Checking the radio system is thefirst thing that I'll cover and is probably the most important. Amalfunctioning radio system can potentially cause more damage than any othercomponent on the vehicle due to a runaway crash. It is very important toperform 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 glitchingor binding in any manner.
Note that the front of the truck should be liftedup to get full steering range due to the zero-scrub steering design. Thisdesign 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 tolock.
Next, make sure that the slide valve in thecarburetor is returning all the way back to the preset idle position and thatit is operating smoothly.
After checking the servo functions, perform a rangecheck with a friend.Make sure that there are new batteries in the radio systemand that the antenna mast is fully extended. Turn both the truck and thetransmitter switches on. Now, have a friend walk away with either the truck orthe transmitter to the farthest distance that you plan on operating the truckand operate all radio functions. All three channels should work fine. If thereis a range problem or the system is glitching do not proceed to operate thetruck until the problem is diagnosed and corrected.
There are many things that can cause radio interference outdoors like powerlines, large outdoor antennas and CB radios. If you are trying to run indoorsthings such as metal beams, fluorescent lamps and computer monitors can causeinterference. Before you think that the radio system is faulty, try anotherlocation and see if the problem clears up.
After checking the radio system functions there are a few things tocheck over before firing up the engine for break-in. Here's a quickchecklist:
- Make 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 engine.
- Check the connections on the EZ-Start®. Make sure that the positive and negative wires are connected to the proper terminals and are secured to the electric EZ-Start® motor. Also check the connection between the blue glow plug wire and the glow plug. The wire should be snug on the glow plug and then inserted inside the protective slot of the head protector.
- Make sure that you use the antenna tube and install it in the molded post on the receiver cover. Do not leave the antenna wire coiled up under the body or wrapped around the body mount. This will shorten the range of the radio system tremendously, which can lead to a runaway.
- Here's a handy tip, slide a zip-tie through the slot at the end of the fuel tank lid so that the long end of the zip-tie is pointing upward. This will act as a handle so that re-fueling the truck with the body on is much easier.
=- 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 andSettings:
Now that you have checked over your T-Maxx and everything is ready to goit's time to break-in the engine. I'll go over a few common problems that mayoccur and how to fix them, and possibly avoid them in the future.
Factoy break-in (default) carburetorsettings:
A good starting point for the TRX 2.5 or 3.3 hi-speed needle is 4 turns out (counter-clockwise) from closed.
Low-speed needle
Idle stop screw
Idle gap
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.
The carburetor is preset at the factory forbreak-in. The base setting should be right to start and run the engine throughthe break-in process. However, if you are having trouble getting the enginestarted or keeping it running, then you may need to readjust the fuel mixtureto compensate for factors such as temperature, humidity, and altitude (airdensity). It is a good idea to bring the little tuningcard that was attached to the fuel tank with you.
(click for larger view)
(click for larger view)
This is a very informative card and will beextremely valuable, especially to those of you that are new to nitro RC. Youcan tear the card at the perforation and place it in your wallet or pit box. Iwish that I had one of these when I got into nitro many years ago. It would'vesaved me from many hours of frustration.
Starting the Engine - After filling the tank with fuel, install a freshlycharged battery into the EZ-Start® 2 control box. Turn the transmitter and thetruck on. Plug the EZ-Start® controller into the receptacle located in themiddle of the rear body mount. Note that the controller will only key into thereceptacle one way. Do not immediately prime the engine. Priming the engine isonly necessary if the fuel is not making its way to the carburetor. Press thered button on the controller. This will spin the engine over while heating theglow 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 aproblem with that function.
The EZ-Start® should turn the engine over at a sufficient enough rate todraw the fuel into the carburetor within a reasonable amount of time. Look atthe fuel line and watch the fuel make its way up to the carburetor. To helpspeed up the fuel to the carburetor you can prime the engine by placing yourfinger over the outlet of the exhaust pipe for just a brief second or two. Youcan see the fuel work its way to the carburetor very rapidly. Caution: Primingthe 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 andoverload cutoff circuitry. This feature will keep the EZ-Start® motor from overheating.
There are two ways to lock an engineduring start-up:
1) 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.
2) 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 sticking.
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 unstuckfrom the sleeve. Before trying to restart the engine replace the starterbattery with a freshly charged pack or a freshly charged battery pack of betterquality.
If the button is pressed too long after the engine stops turning over, thecontroller will stop sending power to the electric motor. When this happens themotor LED on the controller will not light. This means that the thermal cutoffcircuitry was tripped inside of the controller. Allow the EZ-Start® controllerto cool for 5 to 10 minutes before trying to start the engine again. If theengine 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 aneasy process.
1) 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.
2) 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 gasket.
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 immediately.
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 tostart moving. Go ahead and drive the truck slowly back and forth to make surethat the truck is tracking straight and that the engine is idling down when youlet off of the throttle. If everything is in order then carry on with thebreak-in procedures.
If the truck is not tracking straight and the steering trim on thetransmitter is not correcting the matter, then try adding a little bit oftoe-in to the front and/or the rear of the truck. Making the turnbuckle links alittle longer will increase toe-in.
This will give the truck more stability. If theengine 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 thehi-speed needle 1/16 of a turn until it stays running. Keep in mind that theengine will provide strong performance even at a rich break-in setting, sodon't get carried away with mixture adjustments at this stage.
Follow the break-in procedure as outlined by the manual and you will berewarded with a faster and longer lasting engine to show for it. If the engineis idling at a high RPM or is accelerating extremely fast, then the mixture istoo lean for your driving conditions. Richen the hi-speed needle 1/8 turn untilit idles down immediately and is spitting a little bit of raw fuel out of theexhaust pipe.
After completing a few tanks of break-in you may encounter a situation wherethe engine will have a hard time starting or will want to die shortly after itis started. This is typically caused by a fouled glow plug and is common whilebreaking in a new engine. There are tiny particles that pass through thecombustion chamber during the break-in process that come from all of the newcomponents wearing in together for the first time. These particles can foul theglow plug.
Replacing the glow plug with a new one will bring the engine back to life. Iget a lot of questions about which plug to use in the new engine. I recommendusing the #3232 or the 3232X Traxxas plugs exclusively with the new TRX2.5engine. They have a thicker element that will stand up to the extremities ofthe new engine. The #3230 plug should be reserved for situation where a hotterplug is needed, such as running in cold weather conditions. TRX 3.3 Racingengine also runs great on 3232 or 3232X glow plugs.
Be sure to complete the break-in process before tuning the engine in forperformance. Once the fifth tank is completed, bring the truck in, and shut theengine off to allow the engine to cool. Give the truck a quick check over. Ifthe engine ran fine through the full five tanks of break-in, then I like to goahead and change out the glow plug with a new one at this point. Give the trucka good look over for loose screws and make sure that everything is still inorder as mentioned in the above checklist.
Tuning the TRX 2.5 or 3.3 forPerformance:
Hi-speed needleadjustment - After running the truck through the five tanks ofbreak-in it is time to tune the engine for performance. The engine produces alot of power even at a break-in setting, but that's just the beginning. Startthe truck up and make a few passes back and forth gradually giving the truckmore throttle. Once you've made four or five passes back and forth, the engineshould be up to a good tuning temperature, (I'll speak more on enginetemperature later in this segment). Lean the hi-speed needle by turning theneedle clockwise 1/16 of a turn and make a few more passes.
This should increase the power output of theengine. The engine should accelerate very quickly and rev up to a high RPMwithout cutting out or running erratically. Remember, more lean doesn't alwaysmean more power. Tune the needle until you reach peak performance.
When you let off of the throttle, the engine should slow down to areasonable idle without jerking the transmission into gear. Also, the engine'sRPM should not jump up and down when sitting at idle. The engine should idlesmoothly without engaging the transmission and without dying.
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 fewmore passes. You must make a few high-speed passes after each needle adjustmentto determine what the engine is going to do. As you lean out the mixturesetting, the engine may want to idle at a higher RPM. If this happens decreasethe engine's idle by turning the idle stop screw counter-clockwise until theidle comes down to a reasonable level as described above.
Remember that you should always see a puff of smoke from the exhaust pipeunder acceleration. As the truck builds speed the trail of smoke will becomeless noticeable, but should always be there. If the smoke is gone, then thatmeans that there is an inadequate amount of lubrication going through theengine and this can cause permanent damage to the piston and sleeve. If thishappens, richen the hi-speed needle � turn until you see smoke during yourhigh-speed passes and the engine should get back to running and idlingreliably.
If you have found yourself turning the hi-speed needle every which way andhave lost track of the setting and you are having no luck with getting properperformance, take a deep breath and relax. Shut off the engine and think of ahappy place. Don't feel bad. Believe me, we've all done it at one time oranother. Turn the hi-speed needle all the way in just until it stops.
Back the needle out four complete turns. This is a good starting point forbreak-in, which will put you back to where it was when you pulled it out of thebox. The base setting for the low-speed needle is when the adjustment head ofthe needle is set flush with the metal housing that surrounds it. Always startrich and tune for performance.
Low-speed needle adjustment- Once maximum performance is attained out of the hi-speed needleadjustment, it is time to adjust the low-speed needle.
It 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 tothe engine idle down. If the engine is "hanging up" or taking a while to idledown to a reasonable RPM, then the low-speed needle could be too lean.
Remember to try and get the idle down by adjusting the idle stop screwcounter-clockwise first. If the low-speed needle is too lean, then the idleadjustment will not have much of an effect on the idle. Turn the low-speedneedle adjustment counter-clockwise a little at a time until the engine RPM iscomes down to a reasonable level.
The idle of the engine is affected by both of the needle adjustments and theidle stop screw. The low-speed needle has a greater effect on the idle speedthan the hi-speed needle. One of the more common problems that I see withtuning engines is that some people will try and compensate for a low idlecaused by rich low-speed mixture setting by cranking up the idle stopscrew.
Try to keep the idle gap as small as possible. The gap is usually happyaround the 0.7mm to 1.0mm mark. If you find yourself having to go beyond the1.0mm mark then there is a good chance that the low-speed mixture is a littleon the rich side. If you are turning the idle stop screw out so much that theRPM is no longer being affected but is still too high, then the low-speedneedle is too lean.
Keep in mind that the above conditions and adjustments are usually found inan extreme situation when the truck wants to kick into gear or the engine ishanging up badly. Once you have corrected these problems or if they just simplydo not apply, then it's time to move on to fine tuning the low-speed needlewith the low-speed mixture test.
Before you proceed any further, think about what your truck is doing. If youare already getting excellent power and punch out of your TRX 2.5 and the idleis smooth and consistent, then you need not adjust anything. Go have fun. Trynot to make a huge deal out of getting that "perfect" setting. The TRX 2.5produces so much power that it is not as critical to get that "perfect" mixtureto have a lot of fun with this truck.
Low-speed test - Once the engine is up to a good running temperature, make afew high-speed passes back and forth and bring the truck in. As soon as theengine idles down pinch the fuel line between the EZ-Start® motor and thecarburetor with a pair of needle nose pliers. This will keep you from burningyour fingers on the cooling head. The engine should idle up for 3 to 5 secondsthen try to stall. Let go of the fuel line just before the engine stalls. Ifyour engine falls within the 3 to 5 second range then it should be good togo.
If the engine immediately stalls, then the low-speed mixture is toolean.
Richen the low-speed needle counter-clockwise 1/8 turn and retest aftermaking a few more hi-speed passes. If the engine idles up for more than 5seconds then lean the low-speed needle clockwise 1/16 turn and retest.
Tuning theEngine in by Temperature:
Tuning the engine by temperature is another way toadjust the carburetor to maximize performance. This is something that shouldonly 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 areair cooled engines. Weather conditions, fuel type, ventilation and many othervariations around the engine will change the "happy" temperature for eachengine. I try to discourage nitro owners from falling into this temperaturetrap.
The best way to tune the engine is to watch and listen to what theengine is doing. When the engine is running strong and reliably with plenty ofsmoke coming out of the pipe, then check the temperature at that point. Thisshould be a guide to where the temperature needs to be for that particulardriving condition. Maximum temp for any condition should generally not exceed270 F, but some conditions or high revving race operation may require warmeroperating temperatures.
The temperature can provide good feedback to make sure that you are going inthe right direction. If the temperature goes up but performance doesn'tincrease, then the engine may be too lean. One way to bring engine temperaturesdown is to cut a hole in the windshield directly in front of the engine forextra airflow around the cooling fins. The hole should be around 2" to 2.5" indiameter. This is definitely recommended for anyone running his or her truck ina hot climate.
Conclusion:
If you follow these simple yet effective steps for tuning your new TraxxasRacing Engine, I can assure you that you will have many, any hours of highperformance fun with your new Traxxas vehicle. The power of this revolutionarysmall block engine is incredible. With the right tuning skills the TRX 2.5 or3.3 can offer unbeatable performance and reliability whether you are out at thelocal track or in your own back yard!