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Zenoah carburetor clamp failure:
An unknown number of Zenoah engines came equipped
with carburetor clamps which have failed in flight. Typically,
these engines were provided with a rubber intake assembly which
bolted onto the engine intake port. The carburetor is a press fit
into this assembly, and a circular metal strap-type clamp
surrounds the union of the carburetor to the rubber intake
assemble.
This clamp is equipped with an adjustable metal band
which tightens using a screw. The clamps have been known to fail,
usually at the point where the clamp is bent outward to
accommodate
the screw or its mating threaded fastener, usually a nut.
When
this happens, the carburetor may fall off the engine and dangle
from the throttle cable. In at least one case, the free-swinging
carburetor collided with the spinning propeller on a pusher-type
ultralight, destroying the prop and nearly destroying the
aircraft.
REMEDY:
Replace the older light weight clamps with sturdier clamps. Attach
a safety wire from the carburetor body to the engine in any
installation where separation of the carb from the engine could
allow the carburetor to hit the prop.
IT IS UNSAFE TO FLY ANY AIRCRAFT
WHICH HAS NOT HAD APPROPRIATE MODIFICATION!!!!!
Spark plug cap separation::
A significant number of engine failures have been attributed to
separation of the spark plug high tension lead from the engine
spark plug. This is common in both inverted and upright
installations.
It was especially common on earlier ultralights
using inexpensive spark plug caps.
REMEDY:
Replace spark plug high tension leads with leads having integral
caps, that is, leads which are molded together with the caps. Use
only top-quality lead/cap combinations in which the caps grip both
the spark plug upper electrode but also the ceramic body of the
spark plug. Be sure the screw-on cap of the spark plug electrode
is tight!
Use thread lock compound or solder the screw-on cap.
Finally, use a piece of .040 safety wire as a twist-on clamp
around the spark plug cap.
.
IT IS UNSAFE TO FLY ANY AIRCRAFT WHICH HAS NOT HAD APPROPRIATE
MODIFICATION!!!!!
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