Jet -MIKUNI (type: 4/042) TM/TMX, AMAL ARRECHE - (50)

The main jet is significantly involved in the mixture preparation of the carburettor.
If it is too small, the engine dies off under full load and/or runs so leanly that the piston including cylinder overheats and cylinder damage would be the result.
If it is too large, the mixture becomes too greasy, 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 correct main jet, it is first of all chosen so large that the target is an engine that stutters heavily under full load. Of course it needs some experience, but a nozzle is also quickly changed.

Once you have found such a nozzle you mount a smaller nozzle until the engine does not stutter under full load any more.

This way you already have an ideal basic lubrication which 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 is an engine adjusted in this way, which throttles down very slightly when the throttle is closed again under full load.

Arreche, a Spanish manufacturer of carburettors and carburettor accessories, produces carburettors from Amal and Mikuni (under licence) according to a classic design.

So in the Arche carburettors hexagonal main jets are used, as they are also used in the modern Mikuni TM/TMX carburettors in a rather similar design. Among other things, they are not compatible with each other due to the different threading.

The Arreche nozzles are graduated in steps of five, e.g. 60, 65, 70,,,

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