Jetting CR125 Shifter Kart

The easiest way to get the most performance out of your CR125 shifter kart. Plus a logbook that keeps a note of what worked.

Works out the jetting of Honda CR125 shifter kart engines with Keihin PWK 38 and PWM 38 carbs, from the real temperature, humidity, air pressure and altitude.

ENGINES Stock Moto and Mod Moto, with a clamp-on air filter or an airbox with or without foam, and with or without a fuel pump.

RESULTS The jetting recommended for the conditions and the engine you have set: main jet, needle type and clip position, and pilot jet. The main jet also comes with its real value in decimals. Plus air density, density altitude and relative horsepower. Three fine-tuning adjustments of ±10% on high, mid and low to adapt it to your engine and how it is built. The values assume a #6 slide.

CONDITIONS The weather data, two ways: from the nearest public station, with how far away it is and how old the reading is, or typed in by hand. It works just the same with no signal.

TRACKS 143 tracks built in, starting with the ones in the United States. Pick yours and the altitude fills in on its own: the altitude of the track itself, not of the town, which are usually different. Search by the track name or by the town.

ENGINE Engine class, airbox, fuel pump, oil mix ratio and track type.

LOGBOOK Saves every run with its conditions and its jetting, and afterwards you note what you actually fitted and how it went: lean, good or rich, separately for low, mid and high. Laps, best lap and maximum RPM too. It exports to CSV and moves from one phone to another.

UNITS Celsius and Fahrenheit, metres and feet, and mb, hPa, mmHg and inHg for pressure.