Did you actually clean the carb according to the instructins on Outdoor Power Equipment carb page ?
If you really did then remove blower housing and check that the carb is done up tight then start mower and saturate the entire manifold area , including the throttle butterfly shaft with WD 40 or similar .
Work the throttle governor shaft with your finger .
Watch exhaust and listen if you see white smoke or hear abnormal engine noises then you have an air leak
one in 10,000,000 will be a different cause but most are insufficient fuel supply or air entering after the main jet .
