I have a lesco walk behind 48" deck,mower runs great until blades are engaged then bogs the power down,does not die just bogs.have cleaned carb,new plugs,new oil ,fresh air filter and pre filter.all pullys are greased and spin freely.

Hi,
It sounds like you are running on only one cylinder. A check of the plugs ought to have one gray and ashy(the running cylinder) and the other black and wet.
Peace,
Clarke