Your Sirio should flip the truck over backwards when applying full throttle! I don't want to tell you to lean it out, without seeing what else might be going on. But the performance should be 'eye popping'. Check to make sure nothing is slipping, or that your tranny is stuck in 2nd gear.
It's quite possible that you are simply too rich. Main needle must be set first. Low speed adjusted after the main is properly set.