I had one on my 1200GS think they called it the Accelerator Module and were for sale back in the late 2000s
Its basically a resistance that goes inline with the Air temp sensor
Makes the ECU think it is colder than it is and allows the mixture to be enriched
The modern equivalent is the booster plug with an extra probe to adjust for temp variance
Good tool but a tad expensive for what it is The booster plug NOT this I mean!!