How to Fix Too Lean or Too Rich Nitro Engines

Nitro or glow engines use a special kind of fuel, called nitro fuel, in order to function. This is actually a mixture of fuel and air that runs through the engine.

For the engine to function properly, the perfect mixture of air and fuel is necessary to keep the engine running. This mixing actually takes place in the carburetor, an essential part of your RC car. If you don’t get the right mixture of fuel and air into the engine, your RC car might become overheated and blocked from vapor lock. It also causes excessive wear and causes the engine to stall.

There are two types of problems that might arise from the wrong proportion of fuel and air. The first one is a too lean engine and the second one is a too rich engine. Too lean out or to richen an engine means to adjust the mixture of fuel and air. If you want to lean out an engine, you have to add more air to the mix. On the other hand, if you want to richen a nitro engine, you should add more fuel into the mix.

Before you do that though, you should know how to detect these problems. Here are the symptoms of a too lean engine: it dies at full throttle, maybe the glow plug turns white, the engine is too hot, or it dies while the RC car is just idling or accelerating from idling.

On the other hand, an engine which is too rich blows a lot of blue smoke from the exhaust pipe. Also, a lot of unburned fuel exits the exhaust pipe. An engine which is too rich never reaches full top speed and has a cold temperature.

What happens when you lean out or richen an engine? In the former, you will be adding more air to the fuel/air mixture. This action will provide your RC car with a little more horsepower, but, on the downside, it will cause very high temperatures. These temperatures will quickly wear out your glow plugs or cause massive damage, such as engine failure.

In the latter situation, as we said above, you will be adding more fuel to the mix than air. Unlike the leaning out, this situation will give cooler engine temperatures. This setting can be useful in some races, but don’t overdo it because you will bog the engine down and flood it.

So, how do you do it? This operation involves the adjustment of the high end and low-end needles on the carburetor. In order to determine if the low end or high-end mixture needs some tuning, you should allow the engine to warm up and let it stay idle for one minute. If it continues to work, then the settings you have are correct. If this is not the case, you should try changing the settings of the low-end needle. But, first of all, you need to listen to how the engine dies in the test. If the engine’s revs up at the last second before it dies, you are running too lean, so turn the low-end needle/screw counter-clockwise just a bit and retry the idle test. If in the idle test the engine dials down and you notice a change in the exhaust sounds in the last seconds of the test, your engine is running too rich. You should correct this by turning the screw/needle clockwise for about 1/8 of a full turn and try again.

For the high-end needle adjustment, you should “listen” closely to how your acceleration works. If you hit the throttle and it takes off a bit suddenly and afterward it quickly dies or loses power, then your settings are too lean. Try to move the needle counterclockwise 1/8 of a turn and then try again. If it bogs immediately, it is too rich and you need to change the mixture by turning the needle clockwise just a bit.


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