Hello Ira
"altitude-mixture compensation kit for Bing 64 carbs"
Search my name and mixture in archives and you will find what I am doing
for my 914 which will work pretty much same for 912 or 912S except for the
enrichment below 108% power.
I purchased a 912 kit from Greensky primarily for the needle valve. I will
not use most of the hardware and lines, better quality is to be had. The
needle valve is OK except the engraved front is not very nice, will cover
face with engrave placard.
One thing to consider is if you adjust mixture for cruise and at altitude,
if you forget to enrich when you pull back throttle, since there is
greater vacuum downwind of the carbs at the crossover tube at lower
throttle setting, and you have this plumbed to your float bowl vent, you
will run plenty lean and can quit the engine.
Not as bad on the flip side, if you adjust mixture for a low throttle
opening, when you advance throttle you may not be lean enough. This
scenario far more critical for a touchy 2 stroke, but still good to keep
in mind.
Besides having 2 EGTs, 1 for each side, I am installing a Split Second
Mixture Monitor that is run off a O2 sensor. You will see a lean mixture
right away.
I have quite a bit of experience fooling with motorcycle carbs. I have yet
to find vent hose that holds up as well as OEM. Lockwood wants something
like 68$ a meter for Rotax vent hose. They made an error and will not
listen to reason. LEAF wants 68$ for like 10 or 12 feet. That is still
outrageous, but probably what Rotax meant. Anyway I broke down and bought
some. Before doing though, I ordered at least a half dozen 1 foot samples
---From McMaster, close but no cigar for such an important mission of a hose.
I more thorough thought through install on a 914 compared to 912 or 912S.
In the event there is a leak anywhere on the lean side of things, if I hit
my enrichment button it will bypass the whole circuit and at worst run
just a bit rich.
You would be well advised to consider purchasing and installing some sort
of fail safe in the event of a leak.
You see with the mixture monitor you can at least tell if you are rich or
lean. With just a EGT and you are running just a bit lean for any number
of reasons, you may not know that you are lean.
Under no circumstances use the tygon tubing that Greensky sells and
jeopardize your beautiful bird.
1 solution would be to purchase and use a 914 solenoid that toggles
between ambient pressure and the needle valve.
You could even rig a circuit where if the output of the O2 sensor was
anything more than a bit lean of 14.7 to 1 it would engage the solenoid
and plumb it to ambient pressure. If I find it is all too easy to kill the
motor when adjusted for high altitude cruise and pulling throttle at a
lower altitude, I may consider this as well.
I will install a restrict near the manifold connection just large enough
to allow needed lower pressure compared to airbox pressure. In the event
there was a leak in the circuit and I bypassed with the rich button, not
too much air would get in the manifold and unto itself lean things out.
I talked to the Guru at Greensky and thought my business plan sounds
reasonable sound.
I have all the stuff to do a ground test on your plane if ya wanna give it
a try.
If you like how it reacts, order up the stuff you need. I would not fly
with it until you have the best hardware, a plan to deal with a leak and a
mixture monitor and at least 2 EGTs.
I am not at all familiar with your "Glass". I would think it may be
versatile enough where it may be able to take an input from a O2 sensor
and display it in a reasonable fashion. If it can, you could use my
Monitor to map voltage versus mixture. Then just purchase a O2 sensor and
Stainless weld on Bung from Split Second.
Ron Parigoris
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