Points for Pilots

Gauge and color-coded valves for synchronization of carburetors The Rotax 912 engine of our Zenith 601HDS, N314LB, ran smoothly from 3,800 rpm to maximum 5,800 rpm since overhaul of the muffler . But at lower rpm, there was some vibration.  Since ignition of the Rotax 912 engine is virtually trouble-free and compression numbers for the four cylinders were almost identical, the cause might be uneven performance of the two carburetors.  For other causes of rough running engine, see posts on gearbox , setting of propeller blades , and ignition cables .  Carburetor Problems Three things can go wrong.  First, fuel-air mixtures in the two manifolds during idle may not be identical.  Second, the mechanical operation of the throttles may have play so that throttle positions can change at random.  Third, the position of one throttle relative to the other may be wrong so that different manifold pressures are produced. The latter effect is most pronounced at low- to mid-range