When working in the engine compartment with the bottom cowl on I generally
stuff paper towels in the 1/2 inch gap between the top of the footwell and
the cowl lest some errant washer or nut drop into this opening and lodge
there out of reach.
In considering this plus the heat ingress through the footwell it seems that
both items might be addressed by gluing a 1 inch wide band of sound absorbing
foam onto the Classic cowl such that it meets the footwell all along its
border adjacent to the cowl with perhaps a short section at the bottom rear
open to avoid trapping of any fluid which might find its way in. This would
help us butterfingered types avoid problems and also keep hot air from
circulating over about half the surface of the footwell. Any heat which
enters into this area should be removed by airflow over the cowl where it
parallels the footwell. In addition, it might help reduce noise passing
through the footwell area. Has anyone tried this approach and if so, is it
worthwhile?
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I recently helped a friend set the carbs on a 912 installed in a Zenith 601
using the dual vacuum gauges supplied by Lockwood. No directions came with
the gauges so we did the following:
1. Set the idle stop screws to achieve equal vacuum readings on the two
carbs. The screws had been carefully set previously by feeler gauge plus 1.25
turns. The setting achieved using the gauges caused one of the screws to be
turned 1/4 turn relative to the other, i.e. they were no longer mechanically
in sync. Idle speed was set to 1600 with the idea that the throttle would be
advanced slightly to 1800 for most ground operations but a slightly lower
idle could be used to aid landing.
It was noted that one cw turn of both idle stop screws caused the idle speed
to increase about 900rpm, that is, the settings are fairly sensitive and the
1/4 turn differential was probably significant.
2. The mid-range was set at 3000rpm by turning the cable adjusters on the
throttle cables at the carbs to achieve equal vacuum readings.
3. The cable action was checked with the engine off to verify that the full
throttle stops engaged simultaneously, using a feeler gauge. The difference
was less than 3 mils. It is unclear what should be done if this doesn't work
out nor is it clear that 3 mils is close enough.
4. The idle mixture screws were turned cw 1/4 turn (two 1/8 turn
adjustments) in an attempt to reduce soot deposits onto the nosewheel fairing
---From the exhaust. This adjustment seemed to eliminate the problem but may
need more time to prove it has truly fixed it. A slight adjustment to the
mid-range vacuum was needed after this adjustment (which did not make a lot
of sense to us - perhaps we had not set it carefully enough initially).
It remains to be seen whether the initial complaint - slight roughness above
5200rpm in flight - has been addressed by all the above fiddling.
Any comments about how to set up the carbs (with or without vacuum gauges)
would be appreciated.
Regards, John A044
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