ThunderPress East

EAST APRIL 2018

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77 www.thunderpress.net THUNDER PRESS April 2018 Here's a photo of a "lab rat" CV with two Intelajets installed, one in the body of the carb, the other in the adaptor bolted to the intake. You wouldn't (shouldn't!) want both (at least not like this) but it gives you a sense of the installation options. Once installed in whatever manner, you drop three main jet sizes, mount the controller and its air fi lter (smallest in the world, I think) and you can toss jetting slide rules and the angst of re- jetting… away. Intelajet/Dial-A-Jet takes over and jetting issues become pretty much non-existent. …as opposed to this adaptor-type installation on another 45… completed and in action! Here's a "double" done on purpose, correctly and for good reason… on a Mikuni HSR45. Intended for use on a monster motor. Note the install is done in the carb body… their choice or blind faith in advertis- ing where every company builds the "best" performance pipe. Most of the time you can get in the ballpark, but perfection remains elusive. (Look at some crude illustrations close by, with brief explanations of why.) Last but not least—carbure- tors—the very defi nition of close but no cigar about 90 percent of the time. Ironically, not that many riders seem to mind. Maybe that's because it's so diffi cult to predict (let alone master) the intricate interplay between all the components of a build, particularly the infl uence of an exhaust. Maybe it's because even if you get lucky under "controlled conditions" it can all go haywire under different circumstances. After all, the motorcycle won't even operate without the air/fuel mixture a carburetor provides but the known compromises in that simple fact are responsible for the outcome. It is what it is. Or is it? Carburetors are the only compo- nent in a build, designed… intend- ed… to be adjusted. In effect, the single item best suited for tuning the entire package of parts. Evident in the myriad of slides, springs, jets and needles available for each area of car- buretor function, it's almost overkill. In each area of fuel/air supply, from idle to wide open throttle, there's functional overlap. There's also the potential for gaps and imprecision. The Harley Keihin CV carb, for instance, is about as close to correctly set up as a carb is likely to be, when it's attached to bone-stock, emissions- controlled engines. We perceive that to mean, OK at idle, lean from ¼ throttle to near ¾, and on the money wide open, where emissions aren't measured and don't much matter. Runs fi ne, then there comes the pipes and the air cleaner and whatever else you choose and… re-tuning! Which almost invariably is done incorrectly. If not because of the tendency to jet rich for no good reason, or any of the other predictable lapses in judgment or verifi cation… then it's liable to be because of an un-tunable exhaust. Forces you to tune the crap outta the carb, just to compensate. Let alone deal with the breathing characteristics of those heads, cam(s) and manifold! Gorillas in the mist Given its impact and importance, the prospect of improving the state of tune of any given build (involv- ing a carburetor) is not to be ignored! Particularly, if the prospect includes an "on demand" function that deals with those pesky variables and defi ciencies without requiring any tedious "help" from… ah… you. Last month's col- umn introduced a couple of products that go about doing what's needed with a whole different concept. A cir- cuit that supplies a pre-atomized air/ fuel mixture… a light mist… in tan- dem with the circuits already on the carb. This air/fuel mist moves almost as fast as thin air, much faster than fuel, and corrects the lean "bog" that occurs when the throttle gets yanked open. A quick study of so-called back pressure in the exhaust indicates this circuit is also capable of smoothing out pipe pulses that interfere with normal carburetion… which they do! Ditto the turbulence in the intake manifold. In essence, this circuit will fi ll and smooth the air/fuel curve, which makes more torque, which in turn makes more horsepower through- out the engine's rev range. Factor in extra-rapid throttle response and you have the veritable 800-pound gorilla… thanks to the mist. To paraphrase some of the com- pany's technical info: A load must be placed on the engine for the circuit to function. You can't just rev your engine up and watch fuel go up the lines. Without loading the engine, there is no need for extra fuel, so the circuit does not deliver fuel. Three things trigger the circuit: 1) engine pressure drop (like a VOES switch), 2) acoustic/sonic signals which either amplify or dampen the reversionary pulse waves in the intake tract (same physics as exhaust), and 3) air fl ow volume and velocity. The circuit works from just above idle all the way to full throttle, feeding atomized fuel/air mist in linear propor- tion to engine load. Various speeds and engine loads require rapid changes in your fuel/air curve. The circuit auto- matically monitors your engine's needs then instantly alters the air/fuel curve to match. Which means being jetted properly, whether you are pulling a heavy engine load or just cruising. A word about "being jetted prop- erly:" Since the circuit is operating in conjunction with circuits already in the carb, a reduction of main jet size is required because you have two tan- dem circuits now. And… because you can jet for Denver (5,000 feet) or even higher, yet not run lean at sea level. As this is written "the circuit" comes in two forms for Harley carbs. The Dial- A-Jet once drilled, tapped and screwed into the carb has fi ve settings—not adjustable "on the fl y." The Intelajet is more fi nely adjustable, as well as offering two basic mounting options… directly in the carb body… or installed via a bolt-on adaptor sandwiched between the carb and the air cleaner. Go to thunderpress.net to see where your next ride might take you

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