Fuel is still being injected when you take your foot off the throttle, otherwise the engine would die like turning off the key.
If you increase fueling to the point of it smoking you might gain a little power, but you will pay the cost in fuel economy any time you play. Blowing smoke is also an indication of high EGTs. Even if EGTs are not dangerously high, under-fueled is ALWAYS better for engine longevity.