The carburetion on most control-line engines is a simple fixed-size orifice (venturi) with only a mixture ratio adjustment. The engine can be run over a very wide range of mixtures and adjusting the needle valve can be used to adjust the engine speed over a small range. Once released, the engine runs at a more-or-less constant speed until the fuel runs out, or, if equipped, the fuel-shutoff is activated. Altering the size of the venturi used can be used to adjust the gross power. Two-stroke glow motors can be made to run in a 4-stroke mode where the engine mis-fires on every other stroke, and changes mode of firing based on load of the propeller. A tremendous degree of control over how the engine runs in flight is possible by altering the fuel contents, propeller size, pitch, and pitch distribution, venturi size, compression ratio of the engine, and the length of the tuned exhaust, if used.