Jetting for Mikuni CV

The most complete app for tuning Mikuni constant-velocity carburettors: the BS, BST, BSR, BDS, BDST and BDSR series. It simulates setups and compares them against each other across the whole throttle range, for four-stroke road bikes. This is the carburettor fitted as standard to thousands of bikes between 1985 and 2010: Suzuki GSX-R, Bandit, Katana, Intruder, SV650 and GS500; Yamaha V-Max, YZF-R1, Fazer, V Star and Virago; Ducati Monster and SuperSport; the Triumph 900 series; Kawasaki ZX-6R and ZZR600; and the Aprilia Moto 6.5. WHAT MAKES THIS FAMILY DIFFERENT On a slide carburettor the twistgrip pulls the slide with a cable. Not here: the twistgrip moves a butterfly valve, and the slide is raised by manifold vacuum working against a spring and a diaphragm. That is why the needle works according to what the engine is asking for, not according to how far you have turned the grip. This app was built for this family, not adapted from another. WHAT YOU CAN DO • Create as many setups as you like, with name, colour, notes and date. • See the AFR graph against throttle opening: lean at the top, rich at the bottom. • Compare against your reference setup in three bands — low, mid and top — with the difference as a percentage. • Duplicate a setup to try things without losing the previous one. THE WHOLE CARBURETTOR • Six series and eleven bores, from 26 to 40 mm. • Main jet on Mikuni's round scale and pilot jet, both in steps of 2.5. • 1,325 needles with dimensions from the official Mikuni catalogue: measured, not estimated. • Idle screw in turns out. On this family it sits downstream of the butterfly and meters mixture, so opening it RICHENS — the opposite of the air screw on a race slide carburettor. • Clip position when the needle has one. On this family many needles are fixed height, and the app tells you so instead of offering an adjustment your carburettor does not have. BIKES WITH SEVERAL CARBURETTORS Almost every bike in this family has two or four. The app accounts for it: pick the bike and it splits the displacement between its carburettors, which is what actually feeds each one. A four-cylinder bike with four 36 mm carburettors is not an 1,100 cc engine behind one 36 mm carburettor. BIKE CATALOGUE 140 models from Suzuki, Yamaha, Ducati, Triumph, Kawasaki and Aprilia, with the carburettor they came with. For 26 of them the app also carries the full setting published in the manufacturer's workshop manual — needle, jets, clip and screw — and those bikes read zero: whatever you change is measured against what your bike left the factory with. For the rest it knows the carburettor but not the needle. It is not published in any source we have been able to verify, and we would rather tell you than give you a made-up one. THE NEEDLES • Search by code: type the one stamped on yours. • Needle analysis: pick two, with their clips, and compare the profiles. • Tick which needles and jets you actually have, so the lists only offer you those. WEATHER • Temperature, humidity, pressure and altitude, by hand or from the nearest station. • Air density and density altitude, instantly. • Metric or imperial units: °C/°F, mb/inHg, m/ft, kg/m³. HOW TO USE IT 1. Create your starting setup: engine, carburettor and the weather that day. 2. When one works well, mark it as the reference and note how it behaved. 3. Then create alternatives — more altitude, lower temperature, a different jet — and take the one that fits. ALSO • Help on every screen, explaining what each part does to the mixture. • In Spanish, English, French, Italian, German and Portuguese. • iPhone and iPad. Works offline, except the weather station. The calculation model is empirical and is meant for comparing setups against each other, not for replacing road testing or reading the spark plug. Independent app, not affiliated with Mikuni. Brand and model names are used only to identify parts and engines.