|
The needles used in CV carburetors are always a
source of questions. People often try to draw
conclusions from measuring the needle diameters at
various points, but the problem with that is that
the needles are often different lengths, and that
can skew results in a direction not indicated by the
shank diameter.
Anyway, I've done some limited dyno testing in search of
an answer and
I'd like to share the results. I went with two
popular needles used in late model carbs as well as
the 27094-88 needle (N65C) from the 1988 Sportster,
which is a very popular needle in the performance
community.
The results had a fair amount of variation, I did my
best to pick a result for each needle that was
representative of the average result.
All of these results were taken with the same main
jet, and within a very short period of time between
each other.
The test bike was a bone stock 1999 Buell M2. Stock
CV carb (some jetting tweaks is all), engine
internals are all stock, stock muffler, stock
ignition module, coil, plug wires, and 10R12 plugs.
The carb slide hole had not been drilled and it's
using the stock slide spring. The testing was
performed without an air cleaner in place to save
time.
Notice that the carb always goes lean when the
throttle is first opened, then fattens up as the
rpm's come up, eventually ending up too fat, then it
comes back a bit.
Changing the main jet (which I did a bunch of)
basically moves the whole line up or down without
really changing it's shape.
My general impression is that the needles aren't
terribly far apart. However, the NOKK line is enough
flatter than the others that it's probably the
needle I would recommend. I particularly like how it
richens up faster than the others.
Return to tech articles index |
