How to Tune a Traxxas 2.5

Turn on the engine, and allow it to run long enough for it to heat up to its normal operating temperature; all final tuning adjustments are only effective during normal opening temperatures, when the engine is running slightly rich. A great way to distinguish this is by noticing blue smoke seeping from the exhaust.

Turn the high-speed fuel mixture in 1/16 turn increments to lean the engine. Make a few high-speed passes with the vehicle after each adjustment to push out anything clogging the engine. Take notice to improving performance, then make no further adjustments once performance levels off.

Drive the vehicle through a few high-speed runs to test that the high-speed needle is properly adjusted. Pinch the fuel line leading into the carburetor closed, and observe the engine's behavior; it should run for 2 to 3 seconds, then speed up and eventually cut off. If the engine runs longer than 3 seconds, lean the low-speed needle in 1/16 turn increments, testing again with the pinch test after each turn. If the engine dies instantly during the pinch test, richen the low-speed needle in 1/8 turn increments, reassessing with a pinch test after every adjustment.

Check that the base setting is established for the idle stop screw; it should have a 0.5-mm to 1.0-mm gap between the slide valve and the interior of the carburetor's inlet tract. Use the trim knob on the transmitter to adjust the throttle trim enough that the brakes are applied and the vehicle doesn't lurch forward without throttle. Check that the throttle slide is resting against the idle adjustment screw. Remove the air filter to gain access to the idle adjustment screw, then set the idle speed as low as possible while maintaining reliable throttle characteristics. Turn the screw counterclockwise to reduce idle speed and vice versa to increase it. Return the throttle trim to normal settings.