Nitro Engine Tuning Tips and Guide for the Beginner
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Nitro Engine Tuning Tips for the Beginner

To really know nitro engine tuning will take time and patience.

In theory, I mean by what you read, the process of adjusting the nitro engine carburetor to obtain peak running performance is simple. Reality is quite the opposite.

Adjusting the high speed and low speed needles, setting the idle screw and getting the engine to maintain an idle can get very confusing even for the experienced nitro engine tuner.

TIP: Before you start playing with needle settings, get yourself a notepad and write down exactly what your carb settings are BEFORE you start your nitro engine tuning.
Now if you don’t know what they are, set them to the manufacturers specs. If you don’t have the specs on hand you can start with a basic setting of one turn out on the low speed and 3 out on the high speed needle. Also make sure the idle screw has been fully backed off and then, only put an 1/8 of a turn on it from fully closed throttle.

For those with a new engine you will need to complete your engine break-in first. New nitro engines often run erratically at first and this makes them hard to tune. In most cases 2-3 tanks of fuel through the engine is all it takes for the engine to settle down.


nitro engine tuning carburettor parts

Nitro Engine Tuning - Carb adjustment needles: Photo source


Low Speed Needle – this needle meters the fuel rate from idle to 1/4 throttle.

High Speed Needle – this needle meters the fuel rate from 1/4 throttle to full throttle or wide open throttle (WOT) as it is often referred to.

Idle Screw – with the throttle servo in neutral, this adjusts the throttle position to obtain a constant idle after the high and low speed needles have been set.


Let’s Get into Nitro Engine Tuning

During this tuning period you may foul your glow plug, so it is best to keep a couple of new ones close at hand.

I prefer to start with the high speed needle. Firstly because often you are forced to keep the engine revving to prevent stalling, setting this first takes some of the confusion away about what the engine is doing.
It also clears the engine of excess fuel and other contaminants that can hinder performance and make setting the low speed hard.

This first run will give you a good indication as to what your engine is doing.

  1. When you pull the throttle to full there should be nice trail of blue/white smoke coming from the exhaust.
  2. If your engine wants to stall when at full throttle it is to rich.
  3. The engine seems to run well at full throttle but there is little smoke from the exhaust, it is too lean.

If the engine seems to take full throttle and there is a nice blue/white smoke trail you will want to lean the high speed needle by an 1/8 of a turn (screw it in clockwise) and recheck the run. Did the performance improve or worsen?
If it improved repeat the above step until it worsens, then back the high speed needle out (counterclockwise) to the setting it was at before performance dropped. This step should also be done in conjunction with a temperature gauge, although not completely necessary.

The engine wanted to stall at full throttle. Good sign it is too rich. Screw the high speed needle in 1/8 of a turn (clockwise) and repeat the run. Continue to do this until it is too lean as in the above step.

Your engine is running great but emits a little or no smoke from the exhaust. Good sign it is to lean and probably overheating. To richen the mixture, screw the high speed needle out (counterclockwise) 1/8 of a turn. Continue to do the runs and adjustments until the engine wants to stall at full throttle. Then return to it’s best performance setting with good exhaust smoke.


Nitro Engine Tuning for Low Speed

After the high speed needle has been set the engine is warm and running crisp it is time to set the low speed.

  1. Firstly does the engine idle?
  2. If so, does it idle for a few seconds then stall?
  3. Or does it idle fast?

If the engine idles, even for a few seconds, or stalls immediately then it is to rich. Screw the low speed needle in (clockwise) 1/8 or a turn. Recheck.

Engine idles but is sluggish to accelerate, again slightly rich.

Idles fast. Good indication that it is running lean.Screw the low speed needle out (counter clockwise) 1/8 of a turn. Repeat until you can get the engine idling for 30 – 45 seconds.

There should be no smoke at idle.


Setting the idle screw

Now you have the low speed set, setting the idle is easy.
Screw the idle screw in (clockwise) 1/4 turn. The engine will increase in RPM but the clutch should not engage (the vehicle should not want to move).
With the increase in RPM the engine should continue to fast idle and not stall.

I will not mislead you – personally I combine idle setting with the final adjustment of the low speed needle. For simplicity I will continue to explain as a stand alone setting.

Slowly back the idle screw off to reduce RPM and obtain a continuous idle without stalling.
Do not worry if you settle for a fast idle, so long as the clutch is not engaging it is ok.
As I said adjusting the low speed screw and idle screw together will obtain a continuous idle.

Because you have been writing down all the adjustments you have been making, during your nitro engine tuning, you will now know where your engine runs best and what the settings on the carburetor for this are.
When you become confident all this can be done in a matter of minutes and the adjustments taken mentally and only having to write down your final settings.


Nitro Engine Life

A nitro engines performance and life are reliant on tune and maintenance.
Tune your engine to run at it’s peak performance. Running it too rich just gives you an under performing engine. Thinking it will last longer is counter productive to what you want from your engine. There is also problems with over-cooling.
However running a nitro engine lean to increase performance only results in premature engine wear and over heating.
Adding after run oil to your engine is the best preventative maintenance you can do.

Remember engine tuning nitros is more a hands on learned skill, done by a sense of feel and listening.
Treat what you read as a guide only. Use common sense and most of all have FUN.


Nitro Engine Tuning Video

There are many good videos on YouTube about nitro engine turning. The one below  explains and demonstrates quickly and easily how it is all done.