Basics 101: How To Tune A Nitro Engine Effectively

If you are new to nitro RC cars and want to learn how to tune your engine, or if you are having trouble getting your nitro engine performing well, this guide will show you the basics on how to tune a nitro engine for your nitro RC car.

How To Tune A Nitro Engine Effectively

We will be covering the following:

  • High speed needle settings
  • Low speed needle settings
  • Idle screw for the carburetor

We will also be using the following items:

Tuning the high and low speed needles

The needles control the amount of fuel that goes into the carburetor. The more you open the needle, the more fuel will flow into the carb. The high speed needle is used to adjust the amount of fuel at high rpm.

Turning the needle left makes the fuel richer, while turning the needle right makes the fuel leaner. Always tune from rich to lean. Unsure where to begin? If you’ve already altered the needle, richen the high speed needle two full turns from its fully closed position.

Richer LeanerThe best way to tune is to tune to performance. Instead of making large turns or huge adjustments, you would want to make very small adjustments (around 0.1cm each turn) as you tune the high speed and low speed needles. After each small adjustment, try and see if it increases the performance with a high speed pass. Keep making very small adjustments until you reach the best performance.

High speed needle

To start tuning the high speed needle, begin by doing some laps on the track or just blasting through the yard to warm up the engine. Listen to how the engine sounds on the top end once it is warmed up – the engine should have a slight high pitch sound at high rpm and should have a thin trail of smoke out of the tuned pipe.

Lean the high speed needle if it doesn’t seem to clear out on the top end. Always run the engine for 30 seconds to allow for the adjustments to take full effect.

If the high speed needle is too lean, the engine will be fast as hell at first but will then start to loose power later in the tank.

High speed needle

Low speed needle & Idle screw

The low speed needle adjusts low-rpm fuel flow, while the idle screw adjusts the gap between the carburetor housing and slide or barrel to regulate how much air can enter at idle.

You can start to fine-tune the low speed needle and idle screw for more bottom end and throttle response once you are done tuning the high speed needle and geting the engine up to temperature. Running a slightly rich bottom offers your nitro engine a longer engine life and lower engine temperatures.

We will use the pinch test method to tune the low speed needle. Pinch the fuel line that supplies the fuel to the carburetor while idle, which should cut off the flow of fuel to the engine. You will want to pinch it right before it goes into the carburetor.

Count how many seconds it takes for the engine to die out. If it dies immediately it is too lean, if it doesn’t effect the engine for a while it’s too rich. If the engine revs up and dies all within a 4-6 second range, you’re close to getting a rough tune for bottom end.

Low speed needle

Pinch the fuel lineYou will need to keep the idle screw and low speed needle in sync because they work with each other and if one is adjusted the other will require some adjustment. You won’t have to adjust the idle screw and low speed needle as often as the high speed needle once your idle screw and low speed needle are set.

When you have an engine that is tuned properly, you will have a thin blue trail of smoke coming out from the engine. The trail of smoke will slowly disappear as you go full throttle.

You should tune your engine on a daily basis, and always tune the engine with the first tank you are running that day. You shouldn’t have to tweak it much more during the day after you have it set.

Check the engine temperature while tuning

As mentioned, it is important to keep the engine temperature no higher than 260 degrees Fahrenheit while you are tuning the nitro engine. You can measure the temperature with a temp gun or an onboard temperature gauge . Most engines will operate around 230-250 but higher engine temperatures happens in hotter weather and cooler temperatures happen in cooler weather.


Master the basics of how to tune a nitro engine and understand the functions of the high and low speed needles and idle screw. Don’t forget to tune the needles in very small increments and always have the idle screw set before you make these adjustments. Take your time to carefully tune your engine and it will last longer and perform better.

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