How to Tune a Nitro Car Engine
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.
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.
Step 3. Idle Speed 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 by turning it in 1/16 increments clockwise until an ideal mixture is reached. Make several passes with the RC after each adjustment and note any changes in performance.
- 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 from the engine (not exhaust)
- Hesitation or stalling during acceleration
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 carburettor. The engine should run for about 2-3 seconds, speed up, and die.
- If the engine runs longer than 3 seconds, give the low speed needle a 1/16 turn clockwise. Run the vehicle again and retest. Repeat to get right.
- 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 vehicle again and retest. Repeat as necessary.
- Once the low speed needle is correctly adjusted, the engine throttle should respond very quickly. It is now time to adjust the idle speed.
Pinch Test
Step 3. Idle Speed Adjustment
- This screw is located beneath the oil filter, facing towards the front of the vehicle.
- The idle speed screw is used to adjust the throttle input when the throttle servo is at idle.
- This should be set low enough to keep the vehicle from moving at idle, but high enough to keep the engine running. When adjusting the idle speed screw, counter-clockwise closes the carb, lowering idle speed. Clockwise opens it, increasing idle speed.
- This should be the last thing set up, but if it's obviously too high, there is nothing wrong with adjusting it while tuning.
- Remember, the goal is to reach the point that is just before the point where the engine stalls and cuts out.