Jetting for Keihin PWK/PWM/PJ

The most complete app for setting up Keihin PWK, PWM and PJ carburettors. Simulate jetting setups and compare them across the whole throttle range, for motocross, enduro and trail bikes and any two-stroke running one of those three. The three families share the same needle series, the N427-48, so they share the needle catalogue and the calculation model: what changes between them is the set of bores each one was built in. The idea is simple: mark the jetting you know works as your reference, and the app tells you what to change when conditions change, and what every change does to the mixture. WHAT YOU CAN DO • Create as many setups as you like, each with its name, colour, notes and date. • Read the AFR against throttle chart: lean at the top, rich at the bottom, with every setup drawn on it. • Compare each setup with the reference over three ranges: low (0-25 %), mid (25-75 %) and high (75-100 %), with the difference as a percentage. • Duplicate a setup to try a change without losing the one before. THE WHOLE CARBURETTOR • Main jet and pilot jet. • Needle and clip position, with the needle's own dimensions on screen. • Air screw, in turns out from the seat. • Slide: cutaway height. • Carburettor family and bore: PWK from 21 to 42 mm, PWM 36 and 38, PJ from 34 to 38. • Fuel density, oil mix and ethanol percentage. NEEDLES • A catalogue of Keihin needles with their geometry: tapers, lengths and straight diameter. • Both series: the one for PWK 33-39, PWM and PJ, and the short one for PWK and PE 26 to 28, which take a different needle even when the code reads the same. • Search by needle code or by bike make and model, to find which needle came as stock. • Needle analysis: pick two, each with its clip, and compare both profiles on one chart. • Tell the app which needles and jets you actually have on the bench, and the lists will only offer those. RECOMMENDED JETTING FOR THESE BIKES Pick the bike, the year and the conditions and the app proposes the matching factory jetting, ready to create and fine tune: KTM, Husqvarna, Honda, Kawasaki, Suzuki and Yamaha, from 65 to 500 cc and from 1986 to 2024. The full list of models and years is in the app help. FUEL MIX CALCULATOR Petrol, oil and ratio: pick which of the three you want to work out and set the other two. In litres, millilitres, US or imperial gallons and ounces. One button drops the ratio straight into the jetting. WEATHER • Temperature, humidity, pressure and altitude, by hand or from the nearest weather station. • Air density and density altitude worked out as you type. Humidity counts for the oxygen it displaces, not just for density. • Metric or imperial units: °C/°F, mb/inHg, m/ft, kg/m³. HOW TO USE IT 1. Build your starting setup with the engine, the carburettor and the weather of the day. 2. When you find one that works on track, mark it as the reference and write down how it behaved. 3. From there, create alternatives to see what changes when you go up in altitude, when it gets colder or when you touch a jet, and take the one that adds up to the track. ALSO • Help on every screen, explaining what each setting does and which way it moves the mixture. • In English, Spanish, French, Italian, German and Portuguese. • iPhone and iPad. Works offline, except for the weather station lookup. The model is empirical and meant for comparing setups with each other. It is no substitute for track testing or for reading the spark plug. An independent app, not affiliated with Keihin or Hitachi Astemo. Brand and model names are used only to identify parts and engines.