FOR THE LEAD Part
your way to the Front
Photos by John Cox, Spaulding Products
If you've been
following the excellent articles on the Walbro WB3A carburetor by David
E. Close (NKN July 1997 & August 1997) you know that this carb,
standard issue on Yamahas and other Piston Port 2 cycles, delivers a
relatively constant supply of fuel in the upper RPM ranges.
Unfortunately, your engine requires a steadily decreasing fuel supply as
RPMs increase through the 13,000 to 14,000 range and beyond. At the
upper end of the RPM range, the workload on the engine diminishes and,
among other changes, this lessens it's need for fuel. On top end, the
WB3A just delivers too much fuel for peak performance. For years savvy
tuners and drivers have worked around this by constantly adjusting the
hi-speed needle, richening the mixture in the corners and leaning it
down on the straights. You've probably seen drivers reaching across to
tune the carb, corner after corner, lap after lap.
has raised some questions, both from a driver concentration perspective,
and as a matter of safety. Finding a way to allow the driver to tune for
maximum performance while keeping both hands on the steering wheel led
the clever folks at RR Racing (Reggie, Randy, and Rick Fulks) from
Jacksonville, Illinois to develop what they call the Kwik Set Carb
Adjuster. Most racers just call it the "Carb Trigger." Let's
take a look at it and how it mounts.
can install the Kwik Set with the carb installed on the engine. but it's
a lot easier with the carb off. While you're at it, slip the pulse hose
off the back plate of the carb too. Now begin by removing both the
hi-speed and low-speed adjusting needles. You'll be replacing the
hi-speed needle with a modified one that comes with the Kwik Set kit.
You'll need to make sure this new hi-speed needle turns easily, so first
we'll need to reduce the spring tension on it. Try taking the hi-speed
needle spring and compressing it fully with a pair of pliers. Now slip
it on the needle and screw it in finger tight. If it's still hard to
turn, remove it and hold it in a direct flame until it's cherry red. You
can use a propane torch for this, but a cigarette lighter or even a
match will work. Let the spring cool back down and install it again.
This flame annealing of the spring should make it quite soft. Don't dunk
it in water to cool it or it will become brittle and it'll just snap.
Just let it air cool. You can also get some softer springs ready made
for this application from Two Cycle Technology in Wisconsin. Anyway,
once the spring is handled, screw the modified hi-speed needle in finger
tight. Don't forget to be sure the packing o-ring and the little brass
washer are in place first.
you go any further, here's a little trick the guys at RRR missed. Use a
very thin cutting tool or saw (I like the cut-off wheel in my Dremel
Tool kit) to cut a thin screwdriver slot in across the blunt end of the
modified hi-speed needle. This will make it a lot easier to adjust the
needle position, both when you install the Kwik Set trigger, and later
if you need to adjust the trigger adjustment range.
it's time to slip the Kwik Set pulley over the modified hi-speed needle.
You want the little clip that holds the spring and the string on the
pulley in the 3 o'clock position and the machined slot curving around
the bottom. Properly installed, the pulley should look like it's smiling
at you. Slip it as far down the needle as you can without it interfering
with the throttle arm on the throttle shaft as the throttle moves
through it's full range of motion, fully closed to wide open.
lightly snug down the set screw securing the pulley to the modified
needle. Grasp the pulley and check how easily is turns. If it takes any
effort at all, go back and work on the spring some more. It needs to
turn quite freely for the trigger to work properly.
the pulley is all set, screw the Flex-T low-speed needle back in through
the "smile" slot in the pulley. You may find you need to trim
some of the plastic coating off the shaft of the Flex-T to get it to
turn smoothly. Again make sure the pulley turns freely. Now it's time to
remove the back (pumper side) plate from the carb body. This is also a
good time to check the condition of the pumper diaphram and to clean the
fuel inlet screen. Toss the 4 screws you remove in the old parts bin and
mount the Kwik Set backing plate onto the carb back plate using the
longer screws provided. I like to fit 4 little washers into the recesses
in the carb back plate to get the carb trigger back plate to rest flat
and pull down evenly. Properly installed, the brass compression fitting
should be lined up directly with the 3 o'clock side of the pulley. Snug
the 4 bolts up and thread the string through the brass compression
fitting on the carb trigger back plate.
the first carb triggers came out there was a problem with the return
spring tension pulling against one side of the needle and chewing up the
threads in the carb body. The Kwik Set unit now features it's own little
3rd bearing support, a piece of self-lubricating plastic mounted to the
back plate that has a hole that fits over the end of the hi-speed needle
to support part of the spring load. Set that up next, being careful to
make sure the needle continues to turn freely once the support leg is in
place. Don't let it "lean" against the side of the needle as
you tighten it up or it will bind the needle.
time now for the final initial adjustment of the needle position.
Determine how far you want the hi-speed needle to be closed when the
trigger is fully pulled, then loosen the set screw on the pulley and,
holding the pulley in it's fully clockwise position with the Flex-T as
the stop, use a little screwdriver in the slot you made to first close
the needle completely, then back it off the desired amount. (I told you
that slot would come in handy.) In general, I'd set the hi-speed needle
to be between 1/4 and 1/8 open when the trigger is fully pulled to start
with. Experience will show you if you want it richer or leaner as time
goes on. Now retighten the set screw and you're ready to hook up the
Give it a quick final check. You should be able to pull the
handle easily and smoothly to close the hi-speed needle. Releasing the
handle should snap the needle back to the open position. Remember,
you've given up the option of moving the hi-speed needle setting the old
way, so make sure it works easily with the trigger. With the carb
trigger working, you can richen the low-speed Flex-T needle to as much
as 2 to 2 ½ turns open and still get the engine lean enough to
"sing" down the straights.
be amazed at how easy it is to develop the touch of keeping the carb
mixture right where the engine wants it after just a few laps of
practice. Pull it too slow and the engine will be sluggish in the upper
mid-range. Pull it too fast and it will "sag" down for lack of
fuel. Unless you're completely ham-fisted, you'll feel that
"sag" in plenty of time to avoid sticking it by just feeding
the trigger back out.
you have it; a nearly perfect device for optimizing carb and engine
performance without taking your hands off the wheel. Using it can be as
simple, or as complex, as you wish. Next time we'll talk about the
nuances of using the trigger to anticipate when your engine will want
more fuel, using it for quick "flash-cooling" and other subtle
techniques. See you then.
for the Lead - Part 2
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