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Media
Coverage -
"Dial-A-Jet"
- Motocross Action Magazine
36/39 Carb Mods
How to supercharge your KTM two-stroke
Motocross Action Magazine, founded in
1973 (35 years ago) is the Bible of the Motocross world. More than any
other magazine, they tell it like it is! This is particularly true when
it comes to performance. They have a rating system ranging from one to
a possibility of five stars. Since this rating system began they have
given out less than a dozen five star ratings. Motocross Action has
given a carburetor equipped with Dial-A-Jet a five star rating, calling
it a “Supercharger”.
The
motorcycle the Dial-A-Jet was tested on was a KTM; however, Dial-A-Jets
work the same on any make or model dirt bike, ATV, street bike, scooter,
etc..
P.S. Thanks
Motocross Action!
Lonn Peterson, CEO
Thunder Products,
Inc. (manufacturer of Dial-A-Jet)
DICK'S RACING
36/39 CARB MODS
How to supercharge your KTM two-stroke

WHAT IS IT?
Dick’s Racing’s 36mm
to 39mm carb modification program is the most comprehensive hop-up
project ever developed. We mounted it on a KTM 300XC.
WHAT’S IT COST?
$350.00 (carb mods),
$175.00 (Boyesen RAD Valve)—(916) 722-2373.
WHAT’S IT DO?
Believe it
or not, KTM
mounts 36mm Keihin carbs on their 250cc and 300cc
two-strokes. Their competitors’ two-strokes use 38mm or larger carbs
(even KTM’s 125SX has a 39mm Keihin). KTM’s small carb bore increases
fuel velocity at low rpm to provide nice crisp power, but doesn’t really
flow the kind of fuel needed for the best power output. Dick’s Racing
has a special carb mod for KTM two-strokes that takes the mild-mannered
36mm Keihin and totally reworks it in size and intent.
The Dick’s Racing 36/39 carb mod has five
steps: (1)
Dick
Wilk offset-bores the 36mm carb so that it essentially
remains a 36mm carb below one-quarter throttle, but is a 39mm carb above
that. (2)
The cylinder side of
the carb is taper-bored from 39mm to 42mm for maximum frontal area.
(3)
The intake throat is
radiused to eliminate any flow interruptions to the air entering the
carb bell. (4)
A Boyesen RAD valve
is matched to the carb profile.
(5)
A Dial-A-Jet system is
added to provide a massive dose of fuel when engine vacuum demands it.
Dick’s Racing does all the boring,
polishing and machining necessary for $350 (and that includes the
Dial-A-Jet system).
WHAT STANDS OUT?
Here’s a list of
things that stand out with the Dick’s Racing’s 36/39 carb mod.
(1) Performance.
Amazing! Bolting on
the Dick’s Racing carb is like porting the cylinder and adding an
exhaust pipe. The power increase is so great from mid-and-up that test
riders felt that the carb was worth one gear on the track. This is
a great mod for KTM 250 and 300 two-strokes.
(2) Dial-A-Jet.
Although it looks like
nuclear submarine plumbing, the Dial-A-Jet system is simple in design.
It is powered by engine vacuum and draws its fuel supply from a fitting
on the float bowl. The mixture is controlled by a ratchet-style rotary
dial with five air
settings. The fuel is delivered to the carb throat through an emulsion
nozzle (in the carb’s intake throat). Every
MXA
test rider described
the Dial-A-Jet as a “supercharger,” because fuel delivery through the
nozzle is controlled by engine demand. The greater the load, the more
fuel is dumped into the engine. It is not the same as a Power Jet,
because the Dial-A-Jet doesn’t squirt raw fuel,
but instead sprays an emulsified fuel/air mixture that has been atomized
for instant burn.
(3) Jetting.
On our KTM 300XC, we
were able to run two main jets leaner because the Dial-A-Jet added extra
fuel on demand. The leaner setup (and easy jetting changes made possible
by the ratcheted air setting dial) results in better throttle response
and more power from mid and up. Plus, the Dial-A-Jet’s jetting can be
changed (without removing the carb) in about five
minutes.
WHAT’S THE SQUAWK?
Most
test riders felt that the carb gave up
a little low-end to gain a massive
increase in top-end.
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