Description
The main jet is considerably involved in the mixture preparation of the carburetor.
If it is too small, the engine dies off under full load and/or runs so leanly that the piston and cylinder overheats and a cylinder damage would be the consequence.
If it is too large, the mixture is too rich, the engine runs very unevenly and can only deliver a fraction of its possible power.
Here it is important to find the ideal compromise.
To determine the correct main jet, it is first of all selected from the belly so large that the goal 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 have already 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.
The Mikuni carburettors have been improved over the decades, so that they come very close to the literal ideal of carburettors. In the end, the gasoline is only atomized, of course, but now with a precision that is impressive. An indicator for this is that the Mikuni carburettors cover a very wide range in which they can produce a mixture that is still easy to process for the engine. For example, if the atomisation in a Dell’Orto carburettor from the PHB series was already much too lean, this would not be a problem with a Mikuni TM/TMX carburettor. But a real problem can be seen in this characteristic of the Mikuni carburettors. The atomization quality is so fine that the feedback of the engine, whether the mixture is too lean or too rich, is relatively low. This way you can tune an engine much too lean and ruin it even though it seems to run perfectly. So for this high quality carburettor type you usually need a little longer for a precise tuning which works well in all situations. Usually you can take the carburettors out of the box, install them and don’t have to change/adjust much for the first test drive. Except for a few exceptions (TM27, where you often need the needle of the TM30 models).
- size head: 6mm hexagon
- thread: M5,3 x 0,9
- total length: 11,5mm
- thread length: 5.0mm
- 50 – 200 ( 5er step )
- 210 – 500 ( 10er step )
- 520 -720 ( 20er step )
- Designation Mikuni: 4/042
Used in:
- VM carburettor (not VM carburettor from Piaggio/Gilera series vehicles)
- TM carburettor
- TMX carburettor
Attention: Mikuni TM jets are calibrated by flow per time unit, not by bore size. Therefore, nozzles calibrated via the bore (e.g. Dell’Orto) are not comparable in size and function.
AI-translation
Reviews
There are no reviews yet.