Santa bought me a RTR Nitro, what now!?

OS TG.12
OS TG.12

There are many tuning and start up guides for getting your first nitro car started and running. I’m going to try and get the bigger picture of where and why things may be going wrong for you before you give up or end up with a pull start cord dangling in your hand. It’s a LONG document!! Be Patient or stop reading and take your car to the nearest track and ask for advice where to go to have someone do it for you.

The Nitro Engine

Obviously, for a newcomer to the hobby/sport the first thing everyone wants to know is does it start and how fast it is. It’s probably a better idea to first get to know the model as a whole, and understand the working parts that make it roll.

The run in

What’s this all about and why isn’t it already done for me? A model Nitro motor doesn’t have a piston ring, it uses an engine block liner which acts as the inlet and outlet manifolds as well as the combustion chamber. This liner is matched to a piston and the pair together are very tight when you buy them, in order to have high compression this seal between piston and liner needs to be carefully “run in” or “loosened up”. The idea is that we need slightly wear the liner to allow for free movement of the piston but maintain a perfect seal as well.

Before you break your pull start chord!

The obvious external components of a nitro engine are the heat Sink, the Glow plug, the Engine block, Exhaust manifold and for now look for the Flywheel.

Before you begin cranking over your engine with the pull start chord, try turning over the engine using the flywheel. It’s probably going to be so tight and highly compressed you wont get very far with the glow plug still in place so work in clean surroundings and remove it, being careful not to touch the platinum coil or drop it, and take note that a “standard plug” will have a copper washer, so do not lose it. Conical plugs have a tapered end and do not use washers, these are often found in larger or higher quality engines.

It’s often a good idea to invert your car when doing this as to prevent dust and grime entering the block and if it’s already dirty you need to be clean before doing so. Place it in a clean container and be very careful not to get grime in the engine’s combustion chamber.

Now try and turn the flywheel, you will feel the “pinch”, it’s the piston and slightly tapered liner meeting and likely to stick. Don’t force it, you’ll get it stuck. If it does get stuck or jammed, use a screw driver to “back it out” using the flywheel. You may also want to place a few drops of fuel or even better after run oil into the cylinder to lubricate this part of the exercise.

By now you’re probably getting a better mental image of why “run in” is critical, for the most part, the instructions aren’t very explanatory and often not well written. The key issue here is to remember that this process is what will make the difference in the life of the engine over the long term. The smaller the engine, the less robust it is and more care is required. So how are we going to get around this dilemma?

HEAT is your friend!

The very best race engines are the ones where the metallurgists practice their profession. Heat expands the metals and loosens up the engines. The liners and block are made of different metals and expand and contract at slightly different rates.

A heat gun is very handy at this stage, good hair drier will work too. While your Glow plug is still removed, carefully warm up the engine block and see if the “pinch” loosens up a little, it’s will still pinch, just not as tightly and it’s unlikely you’ll be able to turn over the stroke of the engine with your fingers alone, so don’t try it. Don’t cook the engine, as there are rubber boots on the carburettor that prevent air leaks and you don’t want to deform them, be patient. Your objective is to reach a temperature nearing 70-90c (hot to touch) for an optimal run in temp and getting to know your engine.

The glow plug

Nitro engines are two stroke engines that use a platinum coil in a glow plug to ignite the compressed fuel in the combustion engine. Once you get a nitro engine started, this platinum coil will continue to glow unlike a spark plug, so for those looking for a magneto, stop looking and perhaps use the tool that would have come with the starter kit to carefully remove the glow plug put the glow starter onto the plug an see if it’s glowing but don’t leave it connected, you can burn it out. The glow plugs use a 1.5v battery to make them glow, don’t use any other batteries or it will melt.

Carefully place the copper washer around your glow plug and screw the glow plug back into your heatsink, it should be firmly tightened.

The hobby shop never told me all this…

Would you have bought one if they had? Let’s continue as the satisfaction later will be worth the patience now. Once you’re explored the Engine, run in, later on it’s often a simple matter to get your engine started and rolling, the run in process is the most tedious of processes and many of us in the sport have accepted it’s part of the big picture and know that it would be a put off and pointless for hobby shops to explain the reality of Nitro Engines.

If by now, you are bewildered to the point that it’s too much to handle, then it’s up to you whether you fire it up, get frustrated and it’s very likely that a first timer will break the pull chord and head back to the shop where the model was bought. If this is your case, then find a dedicated RC model motor-sport shop and pay a service fee for them to run-in your engine for you. A general retail store isn’t going to have the knowledge or facility to do this for you.

KEEN to learn!!! Let’s look at the CARBY!

We’ve explored the engine and it’s external components but haven’t discussed the carburetor and how it’s works to deliver a fuel and air mixture to your engine’s cylinder for combustion. The mixture of air and fuel is governed by two main needles and seats (like washers in household taps) that control the FUEL flow. The air is a constant parameter that increases by the vacuum created by the piston on the down-stroke. There’s three primary concepts to grasp.

1) The idle screw, opens the air intake at idle, it also retracts the “BOTTOM” or “LOW” needle allowing more fuel into the mixture at idle.

2) The BOTTOM or LOW needle is used at idle and to control the mixture to improve acceleration. This mixture can be adjusted by either retracting or inserting the SEAT or the NEEDLE. A flat blade slot can either be found at the front of the Throttle cylinder or the rear of the carby body. The latter retracts the seat. Some higher performance engines can have three settings which allow for seat and needle retraction on the BOTTOM.

3) The TOP or HIGH needle is used to control the FULL THROTTLE mixture. This mixture is adjusted by governing the maximum amount of fuel permitted to flow to the engine. It’s the needle on the long protruding stem. This needle isn’t generally used to govern the idle mix if set too lean or too rich.

LEAN = more air in the mixture than fuel
RICH = more fuel in the mixture than air

While it might sound simple the case is that most often it isn’t. Air leaks can cause inconsistency, bad or dirty fuel, dirty air filters or overheated engines can vapourise the fuel and cause bubbles in the fuel line. Experience is the key, a sound understanding of how it works will remove false diagnosis and help you with tuning.

What makes this process more difficult is that fuel mixtures depend on Oxygen in the air, hot days will by default have less oxygen and cold days will have more. The key to success is to know that these needles require only very minor adjustments to compensate for these environmental parameters. Once tuned the engine should only be tuned in 5 degree turn increments. If that’s not the case, you are probably experiencing other issues that are changing the tune of an engine or creating resistance on your crank shaft.

The crank shaft

Nitro engines have a hollowed out crankshaft that scoops the fuel from the carby in through the hollow channel, out the back of the crank and then up through the liner and into the combustion chamber. It’s an unusual arrangement that differs from a conventional engine with separate inlet and outlet manifolds. The crank acts as the second part of the inlet manifold system.

Fuel pressure

Fuel pressure is achieved by using exhaust pressure to pressurise the fuel tank and increase fuel flow at higher speeds. Air leaks are a major cause of problems and rubber seals exist starting with the Fuel tank, the carby throttle boot, inside the base of the carby, the exaust port, and finally manifold and exhaiust. Leaks or faulty seals will ultimately change the tuning of an engines fuel pressure and subsequently fuel and air mixture.


Nitro fuel is a mixture of Methanol CH3OH, Nitromethane CH3NO2, and oil, often Castor oil and/or synthetic oils. The mixtures of fuel depend on various engines. Typically, a .12 cubic inch (.21cc) engine uses 16% nitromethane, .21cubic inch use 25% nitromethane and larger engine can use even more. Oils are used to lubircate the engine and vary from 8% – 12%. Regardless, you should use the fuel mixtures specified by your manufacturer or the advised by an experience Nitro hobby enthusiast.

Fuel does change the way your engine will tune and this often leads to a major difference between the manufacturers default tuning settings and the final working settings. This aspect of Nitro engine tuning is likely to cause the most grief for an inexperienced newcomer. Hence start from the manufacturers settings and don’t take them as gospel unless they specify the type and brand of fuel the use. In which case, they cant foresee the weather and a plethora of other parameters that may be impacting your tune.

Air filters

Air filters are straight forward foam filters used to remove dirt and grime. They need some form of thick oil applied to them to remove the micro particles and there are several products available to achieve this. The air filter is another parameter that you need to keep constant, it’s allowing the air flow and if you change types and limit the air flow rates as too will the engine tune need to be set to compensate.

So you’re still reading? And haven’t tried to start your engine yes?? Seriously!!?

I’ll congratulate your tenacity and patience, I’d assume there’s likely to be an adult with a youngster in the midst wanting to get the car on the road and running… “are we ready yet dad!!?”

Checking your throttle End Point Adjustments

Yes, we’re almost there!! While you have the Air filter removed, turn on the radio and check whether the throttle closes fully, push forward (brake) and see if the throttle doesn’t close more than it should. Pull the throttle open slowly and ensure it doesn’t pull your carby off the engine and opens the venturi fully opening the throttle. Adjust these setting on your radio’s EPA/trim or adjust them using the throttle linkage turnbuckles/ball joints if needed.

Setting default idle

Using the manufacturers settings, allow for the idle gap, it should be around 1mm for most 1:10 engines. This is achieved by screwing in or out the idle screw. It simply pushes against he throttle cylinder (or rotor) to create the gap. NOTE: During the run in process, more idle will be required to keep the TIGHT engine running. And your car should be raised on blocks as not to stall the engine if the clutch engages.

Setting the default TOP/HIGH mixture

For now, this setting should be set richer as you are not yet going to full throttle your engine, use the manufacturer’s settings and unwind by 1/4 turn to be safe.

Setting the default LOW/BOTTOM mixture

NOTE: DO NOT SCREW IT IN ALL THE WAY and be very careful if your manufacturer says to do it, the needle will damage the seat or vice versa if you screw in too hard.

This is the needle or seat adjustment at idle, the manufacturer will specify where the default setting should be. As mentioned earlier, FUEL type may have a lot to do with the final setting and keep an open mind when adjusting this. It’s going to manage the air fuel mix at idle and changes if you add more idle. Once set correctly the engine will have a relatively rich mixture to allow for your engine to be happily lubricated and assists cooling at low revs.

Screwing in: Moving the needle closer to the seat will restrict fuel flow and the mixture will LEAN, the rev’s will rise slowly. The engine will heat up more as well as less oil lubrication is available due to the LEAN mixture.

Screwing Out: Moving the needle away from the seat will allow more fuel to flow and will RICHEN the mixture, then engine will drop in revs and you should see fuel spit from the exhaust manifold and the idle will sound rough. This isn’t a bad thing as your engine will have a smoother idle once the run in process is complete and the engine is LOOSE.


As mentioned earlier, it’s time to warm up the engine using a heat gun or hair drier. evenly distribute the heat around the engine until it’s hot to touch, being very careful that you don’t cook the rubber boots and fuel. Often racers will warm up the heat sink and allow for heat to transfer to the block.

Priming – NOTE: Fuel is toxic and combustible, please be careful!

Priming the engine requires that fuel is delivered to the carby and this can be done in several ways. Regardless of method, you will see fuel being delivered through he fuel lines if they are translucent.

      Cranking the engine while placing a finger on exhaust stinger
      Using a large syringe (without needle) and remove the fuel pressure line and pressurise fuel tank
      Use an antenna tube to blow into the fuel pressure line.
      Place a few drops of fuel in the carby. This will start and likely stall as well. Repeat
Cranking a pullstart

You are not starting a lawn mower, do not use your arm and shoulder. Take hold of the pullstart handle between your index and forefinger, turn your palm upwards and flick your wrist upwards, try not to over use your forearm and elbow as you might pull the chord to it’s maximum and break the pull start. (Repairing a pullstarter, another FYI I will write soon)


      Engine warmed to 60-90c
      Carby Idle set to specification
      Radio Turned on
      Car turned on – Throttle trimmed and at idle.
      Glow plug working, washer and plug screwed in
      Glow starter 1.5v battery charged
      Fuel in tank
      Engine Primed
      Car secured