This is Fox's most recent
carburetor series and was engineered to overcome a few shortcomings
that had become apparent in the previous EZ series. These included
occasional production inconsistencies, mid-range metering problems,
and the inability to work well with external fuel pumps. As well,
the fixed (non-adjustable) fuel metering slot employed in the
EZ series carburetor was not always able to cope with the wide
range of propeller sizes, fuel tank locations, etc. that may
be encountered. This "improved" TN carburetor puts
an end to all of these problems, and then some! Oddly, Fox continues
to supply their .40 size engines with the EZ series carburetor
even though this one works much better. Yet another Fox marketing
mystery? The "improved" TN carburetor is available
however, just contact Fox Mfg. and ask for part # 2600.
While this new carburetor does
bear an outward resemblance to its MKX series predecessor, the
internal workings are really quite different. The basic theory
of operation remains the same as the old MKX series (and TN carburetors
in general), however, this carburetor is cleverly designed so
that it does not depend upon precisely shaped metering slots,
or needle tapers, to achieve good throttle linearity. The idle
needle is of constant diameter (no taper), and a fuel-metering
slot of constant width is employed in the spray bar assembly.
Small variations that may occur during different production runs
should have little effect on operation. Another welcome improvement
is the addition of a rubber seal on the main (high-speed) needle
valve assembly. This will eliminate the fuel leakage that was
common on the MKX series, as well as prevent drawing in extra
air, which could upset mixture adjustments.
Our experience has shown these
carburetors to be pleasant to operate and very cooperative. The
idle needle, in particular, seems to have a broader operating
range than most two-needle designs making mixture adjustments
less critical. Throttle transition and linearity are also much
improved over the previous MKX and EZ series. In our opinion,
this is probably the best carburetor ever produced by Fox Mfg.
and is a definite winner! At this time the improved two-needle
carburetor is available only for .40 size engines. Other sizes
are under development and, hopefully, will be available soon.
Adjustment Procedure
The adjustment procedure is basically
the same as the older MKX series (see MKX page). The only real
difference is in pre-setting the needle valves when the settings
are really messed up. Turn the high-speed needle fully in, then
back it out only 1½ turns. With the throttle fully open,
set the low-speed needle so that it "just" begins to
enter the spray bar. These settings should provide a good starting
point. |