Jetting for Mikuni TM & TMX

Mix calculator. Converts between petrol, oil and ratio both ways: you pick which of the three you want to know and set the other two with your finger. Litres, millilitres, US and imperial gallons and ounces, each field with its own unit. The ratio as a percentage and as 1:n at once. One button sets that mixture on the engine screen, where it feeds the jetting calculation. Also: • Engines with more than one carburettor. You can now say how many, and the calculation uses the displacement each one sees. On a single it changes nothing. • The Aprilia RS 250 joins the catalogue with its two Mikuni TM 34. For it the app knows the carburettor and the needle, not the jetting. • Mikuni catalogue needle dimensions for the TM 32, 33, 34 and 36: the 5FP17, 5FP96, 6FJ40 and 6FJ41 are no longer derived. • Fixed the TMX needle profile: the taper angle was being applied twice over. Factory setups now read much closer to zero. • Fixed the effect of air temperature, which was being counted twice.

The most complete app for setting up Mikuni flat-slide carburettors, the TM and TMX series. Simulate jetting setups and compare them across the whole throttle range, for two-stroke motocross and enduro bikes. It is the carburettor fitted as standard to KTM, Husqvarna and GasGas two-strokes from 2017 —including the 65s, with their TM 24—, and to the Honda CR, the Yamaha YZ125, the Kawasaki KX125 and the Suzuki RM125. If your bike is older than 2017 it most likely runs a Keihin PWK, not this. The idea is simple: mark the jetting you know works as your reference, and the app tells you what to change when conditions do. 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 with the reference over three ranges —low, mid and high—, with the difference as a percentage. THE WHOLE CARBURETTOR • Eight sizes, 24 to 40 mm, each with its own jets and needle. • Pilot jet, in steps of 2.5: half the sizes are half points, and the app keeps them. • Needle and clip position, five positions one millimetre apart, with the needle dimensions in view. • AIR screw, in turns open from seated. Here opening it LEANS, the opposite of the fuel screw on a four-stroke. • Slide cutaway: on the Mikuni it is a tuning part, and it rules between idle and a quarter throttle. THE OIL MIX Picking the bike sets the ratio from its own manual, and it is not the same for all of them: from 1:60 on the 65s, 250s and 300s to 1:30 on the Yamaha YZ125. More oil is less petrol in the same litre, so it leans the mixture, and the app accounts for it. It also has a mix calculator: it converts between petrol, oil and ratio both ways, in litres, millilitres, gallons and ounces, and one button sets that mixture on the engine. THE NEEDLES • Eight needle series; the ones not published are marked as derived. • The code reads right through: on a 6BFY43-74, 43 is where the first taper starts —each point is half a notch— and 74 the straight diameter, 2.74 mm. • Search by code or by make and model, to find the standard needle. • Needle analysis: pick two, with their clips, and compare both profiles. • Tick the needles and jets you have, so the lists only offer those. RECOMMENDED JETTING FOR THESE BIKES Pick bike, year and conditions and the app proposes the jetting the manufacturer publishes in the manual, adjusted to your air: KTM 65 SX (2009-2027); 125, 150 and 250 SX (2017-2022); 125 XC (2021-2022); 125, 150, 250 and 300 XC-W, 250 and 300 EXC (2017); 250 XC (2017-2019); 300 XC (2017-2018); Husqvarna TC 65 (2018-2027); TC 125 and 250 (2017-2022); TX 125, TE 150 (2017-2019); TE 250 and 300 (2017-2018); TX 300 (2018-2019); GasGas MC 125 (2021-2023); MC 250 (2022-2023); Yamaha YZ125 (2006-2021); YZ125X (2020-2022). For the Honda CR125R and CR250R, the Kawasaki KX125, the Suzuki RM125 and the Aprilia RS 250 the app knows the carburettor but not the jetting. WEATHER • Temperature, humidity, pressure and altitude, by hand or from the nearest weather station. • Air density and density altitude worked out on the spot. • Metric or imperial units: °C/°F, mb/inHg, m/ft, kg/m³. HOW TO USE IT 1. Create your starting setup: engine, carburettor and that day's weather. 2. When one works on track, mark it as the reference and note how it behaved. 3. From there, create alternatives —more altitude, less temperature, another jet— and take the one that adds up. ALSO • Help on every screen, with what each parameter does to the mixture. • In Spanish, English, French, Italian, German and Portuguese. • iPhone and iPad. Works offline, except the weather station lookup. The calculation model is empirical and meant for comparing setups against each other, not for replacing track testing or reading the spark plug. Independent app, not affiliated with Mikuni. Brand and model names are used only to identify the parts and the engines.