I agree with Mark – everything indicates that much smaller jets are required with the XS carb., compared to QS/QD. Also, you should limit the throttle travel, as beyond a certain opening no more air can get into the engine because of the exhaust restrictor – opening the throttle further just messes up the mixture preparation as the air velocity past the slide reduces.
Some MicroMax Evo Q&A from Australia:
2.1) 125 Micro MAX
Q: Which upgrades for existing engines are mandatory or recommended?
A: Mandatory upgrades are:
– 18 mm exhaust socket with gasket ring
– Perforated tube silencer with 22 mm elbow
– Squish gap
A: Recommended upgrades are:
– XS carburettor
Q: Is it necessary to install the new Dellorto Ignition System to my existing engine?
A: No, it is not necessary as the Dellorto Ignition System will provide the same engine performance as the
existing Denso Ignition System.
Q: What is the benefit of the new Dellorto Ignition System?
A: More equal engine performance, improved throttle response, easier to use, less manipulation possibilities.
Q: Is there a stop sleeve in the new XS carburettor to limit the opening of the carburettor slide?
A: No, but it is recommended to set the accelerator pedal stop to a 60-80% opening of the carburettor slide
(depending on driver’s pedal length preference).
Q: Will a different maximum opening of the carburettor slide have an impact on the maximum
performance of the engine?
A: No, but the improved ease of applying the throttle might improve lap times.
Q: Will the new 125 Micro MAX specification result in faster lap times?