While you won't notice any lack of performance in warm climates without a properly functioning heat riser, you will experience gas contamination in your crankcase. When the atomized fuel hits a cooler-than-operating-temperature intake manifold, some of it pools up as a liquid and does not burn and ends up leaking past the rings and ends up in the crankcase, contaminating the oil causing inadequate lubrication. Unless your climate is at or around 180 degrees, this will occur until the engine reaches operating temperature without the heat riser functioning properly.
