rc car carburetor

What Does Rich And Lean Mean In RC Cars?

What Does Rich And Lean Mean In RC Cars?

If you have time in the RC car hobby, then you probably have heard the terms “running lean” and “running rich” several times. If you do not know what those terms mean, then I will explain what that means, and why they are important if you have a nitro car or are thinking of buying one.

Running rich and running lean refers to the air/fuel mixture. Running rich means that the air/ fuel mix inside the motor is more biased towards fuel, and running leans means that it is more biased towards air. This has important implications for your motor. running too rich or too lean might affect fuel economy, make your motor smell bad, and it might even damage the engine over the long term.

Thankfully, making the air/fuel mix as balanced as possible is very easy. RC cars come with a carburetor that mixes the fuel and the air, and this carburetor has several needles so that you can change the air/fuel mix. You only need a screwdriver to do so! check below for a more comprehensive guide on how to do so.

How To Know If Your RC Car Is Running Too Lean Or Too Rich

The performance and exhaust smell of your car is the best way to know if your RC car is running to lean, too rich, or just right.

RC cars that are running too rich tend to emit a very particular smell. It kind of smells like acetone or rotten eggs. Another signal might be that the car is producing a lot of smoke. This smoke might burn your eyes and smell like acetone like I said above.

Another signal that your car might be running too rich is if you are using a very high % nitro fuel. If you are used to nitro fuel with normal nitromethane % and suddenly switched to something more powerful, then the extra nitro might contribute to the motor running rich. This might be especially true if your car started misfiring as soon as you started using the other fuel.

When it comes to running lean, the main signal your car air/fuel mix is more biased towards air is the engine not accelerating as strongly as normal. This is because the motor might be lacking the necessary nitro to move forward. If your car stops working while accelerating or even while idling, then the motor is probably running too lean.

Another signal is that the car’s exhaust is emitting no smoke. A well-tuned nitro motor will let out a very small amount of smoke, especially when accelerated hard, but if it doesn’t even when dumping the throttle, that is a signal that the motor is running too lean.

Running rich is much safer than running lean, at least over the long run. Running lean for more than a few weeks will probably negatively affect the motor’s internal components.

How To Tune The Air/Fuel Mix

In order to balance the air/fuel mixture, first you need to know where the car’s carburetor is. I would recommend that you check your RC car’s manual because the carb is going to be in different places depending on the car model in question, but most likely, you are going to find it near the air filter.

After you find the carb, the high-speed needle, also known as the HSN, should be nearby. The High-speed needle is one of the ways to adjust the air/fuel mix. Actually, the High-speed needle doesn’t look like a needle at all, but rather a screw inside a brass casing, and its called the high-speed needle because it adjusts the air-fuel mixture at high throttle output. Turning the screw clockwise will lean the motor, and turning it counterclockwise will enrichen the mix.

There’s a different type of needle called the low-speed needle, which manages the air-fuel mix for low throttle. And it’s shaped like a screw like the HSN, but it’s usually not inside a brass casing like the HSN though. This needle might be harder to find, so it might be wise to check your user manual to see where it is. When you find it, the same rules apply. Clockwise for leaning the motor, and counterclockwise for enrichening the fuel mix.

There’s also something called the idle screw, which adjusts the mix when the RC car is idling. This screw is very sensitive and it’s very easy to do something wrong with it, so I would personally advise to leave this screw alone and just focus on the high-speed needle and low-speed needle.

It’s important to keep in mind that if you are going to adjust the needles, avoid turning the screws too much. A slight twist might make a considerable difference in the motor.

For a more complete guide on how to tune your RC car, click here.

Tuning The Low-Speed Needle: Good Idea?

In the RC car world, enthusiasts have always been unsure about something: is tuning the low-speed needle a good idea? There is a sizable crowd that doesn’t think that is a good idea, and that Is because the low-speed needle is notoriously sensitive. A very slight twist might be enough to stall your car when softly accelerating. So this crowd recommends not touching the low-speed needle at all and leaving it on the factory tuning.

But there’s also another camp that asserts that tuning the low-speed needle is fine, but that you really need to know what you are doing in order to avoid crapping the engine. They also say that there are individual models that are much less sensitive to tuning than others.

In my personal opinion, I think that tuning the low-speed needle can be done without issues, but honestly, 90% of people won’t ever need to touch it or tune it. Tuning the low-speed needle will only serve hardcore RC car indoor racers that need as much performance as possible from their cars and people using nitro fuel with a lot of nitro inside.

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