----- Original Message -----
Sent: Friday, February 06, 2004 5:55
AM
Subject: [FlyRotary] Re: nonEFI fuel
systems
Hi, Ken....I also have been looking
at the Weber carb. Without going into full details, how difficult
is it to add a mixture control to the 48 Weber? Thanks in
advance for your reply. Paul Conner
There are two way to do it, one is
with an air bleed system that bleeds air form the intake to the float bole,
this is what they use on some snowmobiles and I have not tried this yet on a
Weber.
The system that I use is an air ram that
changes the pressure differential between the float bole and the
Venturi.
The ram tubes in this photo are positioned
about 1.5 inches from the velocity stacks, when the ram is closed the air is
drawn only from the air cleaner which is where the float bole vent is, when
you open the air ram it increases the air pressure on the Venturi's and the
float bole vent pressure that is in the air cleaner remains the same so it
draws less fuel.
If I start opening the ram at cruise power setting
setting the tac will start climbing until it reaches perfect fuel mixture
and then it will start to drop as it goes in the lean side and for economy
cruise I drop the rpm about 100 rpm on the lean side, depending on altitude
at say less than 5000 ft if I open the ram wide open if will kill the engine
but at over 12,000 ft it can take all the air without killing it, at 16,000
ft the ram will raise the tac 1000 rpm which is enough difference between
holding alt and coming down and I would have never made it up there without
the ram.
One other thing about the Weber is that its
very high tec compared to crude aircraft or American carb's in that it
is very adjustable and it is very sensitive to pressure changes, if the air
is thinner there is less draw one the main jets so there will be less fuel
drawn in.
This can be adjusted for the particular
engine and application by changing the air correction jets and the emulsion
tubes in relation to the main jets, you can go to a smaller main gas jet and
a smaller main air and the mixture on the top end will remain the same but
it will lean the bottom end and mid range, the emulsion tubes mostly effect
the mid range.
By jetting down to a smaller air correction
jet and smaller main gas jet makes it more sensitive air density and to be
honest I don't think the combination the I am currently running is the best
as I only have 100 hrs flying on the 48mm where I had 1000 hrs on the 51mm
so I had it dialed in much better
Ken
Hi, Ken....thank you very much for taking the time
to both explain your system as well as provide the photo....It's
true...a picture IS worth a thousand words! Paul
Conner
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