If you are reading this article, chances are that you recently bought your first RC car, you learned how to break it in from this guide, and now you are looking at how to tune the carburetor. Achieving the optimal carburetor tuning not only is going to improve your car’s performance, but it’s also going to protect your RC car’s engine over the long term. So it’s important that your car isn’t running too lean or too rich if you want your car to keep working over the years.
And the good news is that tuning your car is a very easy process. In this guide, I provide a step-by-step method on how to tune your carburetor for optimal performance. This guide will work for 99% of nitro RC cars out there. Also, I’m assuming that you already know how to turn on your RC car and have broken it down already. If you haven’t done so yet, please check out this guide.
Step #1: Familiarize Yourself With Your Car’s Carburetor & Needles
The first step is making sure you know where the carburetor and the needles are located. This is going to vary between models, but the carburetor is usually very close to the engine. The picture below shows where the carb is in my Exceed Forza.
Also, you are going to have to know where the needles are. The needles are the way to actually lean or richen the engine, and you are going to have to get a screwdriver to modify these. There are 3 different needles that you must know of: the High-Speed Needle (HSN) the Low-Speed Needle (LSN) and the idle screw.
- The High-Speed Needle is the one that controls the air/fuel mix from partial to full throttle. The High-Speed Needle tends to be very easy to find. It is usually a screw inside a brass casing.
- The Low-Speed Needle is the one that controls the air/fuel mix from idle to partial throttle. This one is harder to find, but it’s usually really close to the high-speed needle.
- The idle screw is the one that controls the air/fuel mix when the car is idling. This one can also be pretty hard to find, and if your car is shutting off as soon as you start it up or if it moves forward without input, then you probably need to tune the idle screw.
That picture above shows the 3 needles that all nitro cars have. In order to lean out the RC car, you turn the screws clockwise, and to richen the mix, turn them counterclockwise.
Know If Your Car Is Running Too Lean Or Too Rich
After you know where everything is located in your RC car, its time to figure out if your car is running too lean or if it’s running too rich. As I explained in this article, running rich refers to the engine running on an excess of fuel, and running lean means that the engine is running on too little fuel. There are a few ways to know whether your car is running too rich or lean, including:
Signs Your Engine Is Running Too Rich:
- RC Car Is Emitting Too Much Blue Smoke: A small amount of blue smoke can be normal when accelerating, but if your car is emitting an excessive amount of blue smoke, then that is a warning sign that you should be leaning your engine out a bit.
- RC Car Has An Uneven Power Delivery: If your car shuts off when you hit the throttle hard or the power delivery is uneven, then the carb might be too rich. Leaning out the engine might be warranted.
- RC Car Engine Doesn’t Heat Up: If your car’s engine doesn’t get very hot, then the engine might be running too rich. This can be pretty hard to diagnose, but most well-tuned RC cars will have pretty similar running temperatures. If your car’s temperature is significantly cooler, then that might be troublesome.
Signs Your Engine Is Running Too Lean:
- RC Car Shuts Down Soon After Its Started Up: This is something that very often happens when first starting a new RC car. If this is your situation, then most likely you need turn the idle screw counterclockwise a little bit. It might be too lean.
- RC Car Engine Is Excessively Hot: RC cars will heat up a little bit when used, but if the engine is so hot that water evaporates as soon as it touches the metal, then that means that the engine might be running too lean.
Depending on whether your car is running too lean or rich, you will have to turn the needles accordingly to balance the air/fuel mix.
Adjust The Idle Screw
If your RC car is shutting off as soon as you turn it on (idle screw too lean) or if it’s accelerating without input when you turn it on (idle screw too rich), then you need to adjust the idle screw.
After you have located the idle screw, slightly turn it counterclockwise to richen the mix. If your idle screw is set too rich, slightly turn it clockwise to lean it out as you see in the picture below.
After you turn the screw, try starting the RC car. If the car starts up without shutting off and without accelerating forward without input, then you have most likely achieved the optimal tuning for the idle screw.
Adjust The High-Speed Needle
After tuning the idle screw, its time to tune the high-speed needle. Now, make sure that you really need to tune this needle before touching it. If the high-speed needle is set too rich, then expect uneven power delivery when accelerating hard. Also, the car might emit a very high amount of blue smoke when accelerating hard. And if the high-speed needle is set too lean, then the car will not achieve its top speeds and it might get super hot at high temperatures.
When it comes to the tuning, the same things that apply with the idle screw applies here: turn the screw counterclockwise to richen the mix and turn it clockwise to lean it out.
Adjust The Low-Speed Needle
After the high-speed needle, its time to tune the low-speed needle, which is usually located on the other side of the high-speed needle. When it comes to this needle, it’s actually really hard to diagnose whether you should tune it in the first place, but a good way to know is if your car has a hard time accelerating when first hitting the throttle.
If you aren’t sure if you should touch this needle, it might be wise to just leave it in factory settings.
Other Useful Things To Know
- Look Into The Factory Carb Settings: Many enthusiasts tend to start tinkering with the needles without knowing what they are doing, disrupting the carburetor. If this happens to you, then you are going to have to look in the factory carb settings. This is usually found on the car’s manual, or in the internet.
- When In Doubt, Leave It Rich: It’s preferred to run your RC car a little bit too rich rather than too lean. Running the engine too lean for a prolonged amount of time will seriously destroy your engine while running too rich will not do so.