Is the yardman mower brand new? Often times when brand new (or when a mower sits for a period of time), you need to prime more than the three times that the label tells you. Above the primer on a yardman you should see a red sticker with something along the lines of "(push 3x)." Small engines suprisingly do not have enough draw to siphon in thier own gasoline, hence why you need to initially prime before starting. Try priming (pushing the rubber suction) about 10 to 12 times to force addtional gasoline into the carb. You may notice an initial puff of black smoke due to the offgass burning of all that additional gasoline. If this problem persists however, look into speaking with a small engine repair shop to further troubleshoot.
Dan
September 2009