When tuning the nitro engine on a RC race car or any other vehicle, it is good to understand
the basic RC parts of a nitro vehicle and their functions.
Make sure to completely break-in your nitro engine prior to tuning the engine for maximum performance.
The main function of the carburetor is to create a proper mixture of fuel and air. Once this mixture is achieved, it is sent to the engine to be combusted. The carburetor can be adjusted to control the mixture ratio of gas to air that is fed into the engine. If you increase the amount of fuel in the mixture, you are making the mixture "rich" and alternatively, if you decrease the amount of fuel in the mixture, you are making the mixture "lean".
An engine's performance is dependent upon this fuel mixture and is regulated by the carburetor, which, in turn, is regulated by a high speed, low speed, and idle speed setting.
Important: Turn the mixture needles clockwise to “lean” the mixture and counterclockwise to “richen” the mixture. A lean fuel mixture will increase engine power, but only in the right moderation. Temperature is a good way to judge how the motor is running, but do not solely rely on temperature. A good range to follow is 210-270F, varying with different motors.
Caution: Never run an engine too lean, because it will cut out or begin to stall. This could cause severe engine damage.
In order to tune your RC for performance, start with a rich fuel mixture and slowly move towards a lean mixture until the ideal mixture ratio is achieved.
Caution: Never tune from a lean to a rich mixture. There should always be a light stream of smoke coming from the exhaust.
You can tell an engine is running rich by observing any of the following:
Leaning the high speed fuel needle increases performance
Unburned fuel spraying from the exhaust tip
Step 1. High Speed Fuel Mixture Adjustment
This is primary fuel mixture adjustment. It is located next to the air filter, where the fuel line connects to the engine.
After the engine is warmed up, gradually lean the high speed mixture needle by turning it in (Clockwise) 1/16 increments until an ideal mixture is reached. Make several passes with the RC after each adjustment and note any changes in performance. At first greater than 1/16 adjustments may be used but as you get closer to the ideal fuel mixture smaller adjustments need to be made.
If you "lean" your mixture too much, one or more of these things may occur:
Fluctuating idle speed
Temperature measurement above 270F at the glow plug
Little or no smoke from the exhaust
Noise or clattering sound during deceleration
Sudden cutting of power during acceleration
Smoke or steam form the engine (not exhaust)
Hesitation or stalling during acceleration
If you are experiencing one or more of these symptoms listed above, slowly richen the mixture by giving the high speed adjustment 1/16th turns counterclockwise until the symptoms disappear. Again is this may need greater than 1/16th adjustments if the motor is greatly showing symptoms of being too lean.
Step 2. Low-Speed Fuel Mixture Adjustment
The low speed mixture adjustment is performed only after the high speed needle has been correctly adjusted.
The easiest way to adjust the low speed mixture is by doing the "pinch" test. The valve is located where the throttle arm pivots.
Having set the high speed needle correctly, take the RC vehicle and pinch the fuel line going into the carburetor about an inch or two from the carburetor.
While performing the pinch test, the RC engine needs to be “cleared out” between pinch tests to burn excess fuel in the engine. To clear the motor out, make a pass or have the vehicle off of the wheels and rev the engine a few times and let the motor return to idle.
The engine should run for about 3-5 seconds, speed up, and die.
If the engine runs longer than 5 seconds, give the low speed needle a 1/16 turn clockwise. Clear the engine and Repeat as necessary.If the test results in the engine dying immediately, without speeding up, richen the low speed needle by giving it 1/8 turn counter clockwise. Run the RC car again and retest. Continue to repeat as until you achieve a pinch test of 3-5 seconds.
Once the low speed needle is correctly adjusted, the engine throttle should respond very quickly. It is now time to adjust the idle speed.
Step 3. Idle Speed Adjustment
This spring tensioned screw is located beneath the air filter on the carburetor, either on the front or the back of the carburetor (dependent on how the carburetor in positioned on the gas RC product).
In order for an engine to run, it must have enough internal inertia built up in the engine to catalyze the entire ignition cycle. Ideal idle speed is the slowest running idle possible, just before the motor starts to stall.
The key is to set the idle speed as low as possible while still maintaining reliable running characteristics. In order to do this, turn the idle screw counterclockwise to reduce the idle speed. If your engine stalls or cuts out, turn it clockwise to increase idle. Remember, the goal is to reach the point that is just before the engine stalls and cuts out.
Tuning can be aggravating, this makes it easier to drive your RC car and more enjoyable to use!