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

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.

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.

34 www.motocrossactionmag.com