Jet -MIKUNI (type: 4/042) TM/TMX, AMAL ARRECHE -

The main nozzle is significantly involved in the mixture preparation of the carburettor.
If it is too small, the engine dies under full load and/or runs so lean that the piston and cylinder overheat and cylinder damage would result.
If, on the other hand, it is too large, the mixture is overgreased, the engine runs very unevenly and can only deliver a fraction of its possible power.
Here the ideal compromise has to be found.

To determine the right main nozzle, it is first chosen so large from the belly that the target should be an engine stuttering strongly under full load. Of course it needs some experience, but a nozzle is also quickly changed.

If you found such a nozzle you now mount a smaller nozzle until the engine under full load no longer stutters.

Thus one already has an ideal basic nozzle that ensures that the engine does not get too little fuel under full load, which it also needs to cool the piston and cylinder. A safety optimum represents such an adjusted engine, which throttles quite easily briefly if one closes the gas again under full load.

The Mikuni carburettors have been improved in the course of the decades always further so that they already come quite close to the literal ideal of the carburettor. In the end, the gasoline is only atomized, of course, but now with a precision that is impressive. One indicator of this is that the Mikuni carburettors cover a very large area where they can produce a mixture for the engine that is still easy to process. If the jetting in a Dell'Orto carburettor from the PHB series were already much too lean, for example, this would not be a problem with a Mikuni carburettor from the TM/TMX series. A real problem, however, becomes apparent especially in this character trait of the Mikunis. The atomization quality is so fine that the feedback of the engine, whether the mixture is too lean or too rich, is relatively low. So you can tune an engine much too lean and drive it through it broken, although it apparently runs flawlessly. Thus one needs for this qualitatively high-quality carburettor type usually somewhat longer for a precise tuning in all situations well functions. As a rule, you can take the carburettors out of the box, mount them and don't have to change/adjust much for the first driving test, except for a few exceptions (TM27, you often need the needle of the TM30 models).

• Size head: 6mm hexagonal
• Thread: M5.3 x 0.9
• Overall length: 11.5mm
• Thread length: 5,0mm
• 50 - 200 ( 5-step )
• 210 - 500 ( 10-step )
• 520 -720 ( 20-step )
• Designation Mikuni: 4/042

Used in:

• VM carburettor (not VM carburettor from Piaggio/Gilera series)
• TM carburettor
• TMX carburettor

Attention: The Mikuni TM nozzles are calibrated via the flow rate per time unit, not via the bore size. Therefore nozzles which are calibrated via the bore (e.g. Dell'Orto) are not comparable in size and mode of operation.

(machine-translated)