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

Cooling shroud and black blast tube for voltage regulator When my friend Mel and I built the Zenith 601 HDS, N314LB, in 1995, instructions for installation of the voltage regulator--to be precise, voltage regulator/rectifier--of the Rotax 912 did not contain any information about temperature limits. Ditto for the ignition module. We first became aware of potential overheating of components by the Rotax Minute - Component Temperatures video available for subscribers of rotax-owner.com .  The video mentions a temperature limit of 176 deg F, or 80 deg C, specified by Rotax for both voltage regulator and ignition module. In our plane, ram air entering the cowl cools the ignition module.  Since that module does not generate any significant heat, and since air temperatures inside the cowl are well below the 176 deg F limit, we are not concerned about that module. A different matter is the voltage regulator. It produces significant heat, as is implied by its cooling fins. Th

Pump System with two Facet pumps and low-pressure switch In 2014, the  19-year old Rotax 912 engine of our Zenith 601HDS, N314LB, had run 1,618 hrs without any sign of wear or significant trouble, with one notable exception: The mechanical fuel pump had failed five times. Failures of the Mechanical Pump Five pump failures within 1,618 hrs is astonishingly bad performance, given that mechanical diaphragm pumps, for example in Continental or Lycoming engines, generally last beyond engine TBO without a hiccup. The pump failures were of two types.  Either the fuel pressure would drop to zero, in some cases rapidly, in others very slowly. Or the pump would leak blue-colored oil, indicating a diaphragm failure where blue avgas was mixed with oil.  That mixture would exit the cowl in front and eventually streak onto the canopy.  The shortest time between failures was 61 hrs, and the longest 729 hrs. Rotax then offered a pump of different design. It has a vent tube whe

Garmin GPS 18x receiving unit Four years ago, with friend Mel's help we installed the DigiTrak autopilot made by TruTrak in our Zenith 601HDS, N314LB. The autopilot requires GPS NMEA 0183 input. To save cost, we supplied that input with the already-installed Garmin GPSMAP 195. In the DigiTrak installation manual, TruTrak advises against that choice since the 2-second update cycle of the GPSMAP 195 is not quite fast enough for the autopilot and may result in wandering flight during turns. That problem did indeed occur, as well as occasional meandering in straight-and-level flight. Recently, the GPSMAP 195 battery needed for retention of user options failed. A replacement battery that nominally should last 10 years failed after eight weeks. Ditto for a second replacement battery. Clearly, it was time to eliminate the GPSMAP 195. Indeed, except for the autopilot, the GPSMAP 195 was no longer needed since the combination of Garmin GDL 39 and iPad installed a year ago produces