Powered Parachute Flying Handbook

Chapter 4 — Powerplants

Two-Stroke Carburetor Jetting

Carburetors are normally set at sea-level pressure, with the jets and settings determined by the manufacturer. [Figure 4-9] However, as altitude increases, the density of air entering the carburetor decreases, while the density of the fuel remains the same. This creates a progressively richer mixture, same fuel but less air, which can result in engine roughness and an appreciable loss of power. The roughness is usually due to spark plug fouling from excessive carbon buildup on the plugs. Carbon buildup occurs because the excessively rich mixture lowers the temperature inside the cylinder, inhibiting complete combustion of the fuel. This condition may occur at high-elevation airports and during climbs or cruise flight at high altitudes. To maintain the correct fuel-air mixture, you can change the main jets and the midrange jets setting for base operations at a high density altitude airport. Operating from low altitude airports and climbing to altitude where the mixture becomes rich for short periods is OK.

Operating an aircraft at a lower altitude airport with the jets set for higher altitudes will create too lean of a mixture, heat up the engine, and cause the engine to seize. The pilot must be aware of the jetting for the machine to adjust the mixture. Consult your POH for specific procedures for setting jets at different altitudes.

 ŠAvStop Online Magazine                                                                                                                                                       Contact Us              Return To Books

AvStop Aviation News and Resource Online Magazine

Grab this Headline Animator