Lately my motor has been acting up. When I rev it up with the blades engaged, it sputters blowwing black smoke too. I have cleaned the plugs, Checked float level and for dirt in the carb. Is it common for the "smart spark" to cause problems like this? It is more common when I get to a lawn, not too often when re-engaging on the same property. (it has 530 hours and air filter is clean as a whistle too) Thanks!