Shawn---Don Malling has posted a very good description of how CD
carburetors work.
Your original post suggested that you wanted to get a better needle for
taking the richness "bump" out of the acceleration curve, as shown by
the dyno and the A/F monitor. All other things being equal, this can be
accomplished with a needle selection that is thicker, but you want this
change to occur only between 2200 and 3,200 rpm. The biggest problem
here is that few of these needles that you see on the chart are
available. (Call Joe Curto to see what is) That's why many of us have
gone with the SU needles, which are available (Burlen Fuel Systems, in
England)
For a good part of 19 years, I had a second home at 6,000 feet, so I am
familiar with what altitude can do to the air/fuel mix. Typically, my
monitor would register one or two LED's richer than at sea level.
However, having the proper needle kept the mix relatively even,
regardless of the rpm.
You have a good tool in the A/F Monitor. I would use it to get the mix
the way you want it before going back to the dyno. If it were me, I'd
start with finding out which part of the needle is too thin, then see if
there is an SU needle that is comparable to the B1AF in all stages
except the one that is "wrong". The SU book has these selections. Burlen
has the needles.
Richard Good may have some needles designed for altitude that would fit
the ZS.
Kastner's book can tell you how to adapt your ZS for the SU needle. So
can the SU book by Des Hammill, mentioned in an earlier post.
Meanwhile, you can tune the timing, reset the valves, try different
dashpot oils and such. If you continue to have the monitor run off the
scale, we can agree that the problem is not solved and power is probably
being lost due to over-richness.
Dick
|