Black smoke coming bullet electra350 uce royal enfield bike

Hi

my royal enfield bullet electra 350 with UCE engine is giving some trouble , when I ride bike it is great but if I throttle it and on high revs I am seeing black smoke coming out of the bike. On slow speed there is no visible smoke and even on fast speed but when I throttle it higher revs .. black smoke starts coming out of the bike. Guide me what is the problem or my bike has developed some serious issue ?

I had recently got is serviced and bike has done only 25000 km on odometer and there was no black smoke but only started coming from 1 week or little more .

please advice me what should I do ?