I have the 2 year old Toro Timecutter 50 inch with the Toro 24.5 hp engine (708cc I think). Issue: runs well at full throttle and with PTO engaged. At idle it begins to bog down and finally dies. It is difficult to re-crank and expells black smoke out the exhaust. I'm assuming it is flooding. I'm thinking first, make sure the choke is not malfunctioning then I'm thinking pull and clean the carb. Am I going at this right or should I first try something else???