Complex sentence: Petroleum-based fuels offered more power than alcohol, but standard gasoline and kerosene left too much silt and combustion by-products that could clog engine plumbing, in addition they lacked the cooling properties of ethyl alcohol.
Split into simpler sentences: Petroleum-based fuels offered more power than alcohol, but standard gasoline and kerosene left too much silt and combustion by-products that could clog engine plumbing. In addition they lacked the cooling properties of ethyl alcohol.