MXA PRODUCT TEST:
DICK’S RACING ULTIMATE FOUR-STROKE CARB
CONTACT? www.dicksracing.com or (916) 722-2373.
WHAT’S IT DO? No matter how powerful an engine, it can’t run properly without receiving the proper mixture of air and fuel for the conditions at hand. Electronic fuel injection has been getting a lot of hype because it’s new to motocross bikes, but experienced motocrossers know that a well-jetted carburetor is tough to beat. When the MXA wrecking crew put Dick’s Racing 36mm/39mm Carb Mods on our KTM 300 two-stoke last year, we were shocked at how much power it added. So, when Dick Wilk told us he had the “Ultimate Four-Stroke Carb,” we had to try it.
ÿÿ The Ultimate Four-Stroke Carb can be broken down into five separate modifications. First, Dick “taper bores” the front side of the carburetor in progressive steps from 39 to 43mm. Second, he installs a Thunder Products Intelajet (formerly known as Dial-A-Jet) to precisely meter the fuel/air mixture. Third, the carb gets an R&D Power Pump accelerator pump chamber and Flex Jet. Fourth, an extra-large, anti-cavitation float bowl nut is installed to provide a generous quantity of fuel. Finally, the carb is rejetted to match the modifications. The result is a highly advanced and highly tuneable carburetor. We swapped back and forth between Dick’s Ultimate Carb package and the stock carb on our 2009 Yamaha YZ450F to put it to the test.
(1) Taperbore. On a 2009 YZ450 FCR carb, Dick taper bores the front side from 39mm to 43mm in an effort to keep the same high fuel velocity of the stocker while adding a claimed 15 percent increase in overall flow. Additionally, Dick matches the intake manifold to the high-flow profile of the modified carb bore.
(2) Intelajet. Dick utilizes the brand-new Intelajet system on its Dial-A-Jet to compensate for the increased airflow from the taper bored carb. The Intelajet accurately mixes the fuel with air and then injects the vaporized fuel directly into the throat of the carburetor. The fuel is automatically regulated by the suction created off the engine, so the higher the load, the more fuel is drawn into the carb venturi. Intelajet is as easy to use as a shock clicker.
(3) Power pump and Flex Jet. The R&D Power Pump has an adjustable leak jet and prevents bogging. The Flex Jet enables fuel screw adjustments without tools.
(4) Rejetting. Rejetting is mandatory with these modifications, because the goal is to get the leanest running bike possible from low-to-mid and then inject a fresh charge for mid-and-up power. When you send Dick your carb, he takes all of the different variables into account, including the type of exhaust system, fuel, air filter, etc.
(5) Adjustability. Dick’s Ultimate Four-Stroke Carb features an adjustable leak jet, a much easier to adjust fuel screw, and a dial that controls the air/fuel mixture (this dial can be mounted anywhere on the bike). We mounted ours in front of the gas cap so we didn’t even have to stop riding to make adjustments.
(6) Performance. With a little fine tuning, our YZ450F equipped with the Ultimate Four-Stroke Carb ran crisply and without hesitation from the first crack of the throttle to the upper reaches of the rpm range. On the track, test riders felt only modest overall power gains, but the real benefit was in increased usability (thanks to the leaner low-end and richer top-end). The Intelajet allows you to run three sizes leaner on the mainjet. The Intelajet makes tuning mid-to-top jetting as easy as reaching up and turning a dial. The adjuster controls the air supply of the unit and has four full turns of range.
WHAT’S THE SQUAWK? Differentiating between the effects of adjusting the Intelajet versus the fuel screw versus the leak jet takes some practice and expertise (most of it trial and error). We went in the wrong direction many times before we got it right.
The Ultimate Four-Stroke Carb will make you question the need for Electronic fuel injection technology.