Actually the change needs to occur from about 2200 all the way to
redline. Even after the power comes back up the mixture stays rich
(right at 11 on the A/F from about 3300 to redline, it drops below 10
between 2200 and 3300). It never cames back to a proper
mixture. Unfortunately the A/F meter was the tailpipe probe while on
the dyno so I can't really work on mixture through the rpm range
before going back to the dyno. Although I have thought about the
benefit of one mounted in the exhaust closer to the engine.
Don did have a decent laymans description of the theory behind CD
carbs and I understand that. The difficulty that I see doesn't really
dispute it in my mind. The needle profile is designed around the
volume of air that must move through the carb body as demanded by the
engine. The B1AF is designed to feed three cylinders with that given
amount of air. Under immediate load the demand for fuel from the three
cylinders is greater than it would be for two but it is still tying to
feed fuel for three cylinders. The taper of the B1AF starts quickly
and then settles into a more linear taper, at least that is how I
visualize the numbers given in the Haynes. So my thinking is that the
ideal needle profile would be a more linear taper.
Regardless, the needle profile, the airvalve, damping fluid, spring
and throat size all must work together to feed the cylinders demand
for air and fuel. They are desinged for specific applications other
wise one needle would be sufficient for all purposes. Adding a third
identical carb to a car desinged for two should theoretically have an
over carb effect. Just like when you put triple webbers on you have to
put tiny jets in them to get them to run right. Too much carb
initially.
Some local LBC people have speculated about using 1.5" carbs instead
of 1.75" but I think that would reduce the air volume too
much. According to Burlen Fuel Systems a six cylinder engine with the
displacement of the TR6 should use three 1.75" carbs. (I read that in
one of their publications somewhere but haven't found it again yet. I
don't think it mentioned needle numbers and of course it was meaning
three HS6 SU's. )
I have been in contact with Richard Good and while helpful. he has not
experienced these issues at his alttitude. I promised to keep him
informed and I'll do the same with all of you. I should also note
that I do not have any dissatisfaction with any of Richards products.
NFI but I am a happy customer. He has also been very good about
responding to any questions that I have posed to him. He is probably
keeping his head down due to all the commercial content posts as we
are discussing one of his Tri-carb set ups with one of his cams etc...
Anyway... This discussion is great. The list has been great and I
welcome any more input and ideas. The weather is supposed to get back
into the 50's again today like it has been all week. As soon as the
frost melts away I think I'll put the top down and spread some
Christmas cheer LBC style and enjoy the sound of my engine and it's
poor fuel mileage. Running rich or not that broad flat torque curve
is an awful lot of fun to drive. :-)
Shawn
Merry Christmas everyone...
|