Yanmar designs it engines with the filter size of 2 microns to protect the fuel system high pressure pump and injectors - this is why the small filter mounted on the engine is fitted with the 2 micron element. The Racor or other brand filters are usually added at the the time of engine installation and can be whatever you want. If you put a 2 micron element in the Racor, you will never have to change the filter on the engine, but you will change the Racor more often. 30 micron is a 'coarse' pre-filter and you will have to change both the Racor and the on-engine elements at regular intervals. Because the Racor is way over-capacity for my 30 HP at 500 GPM, I compromise and use a 10 micron filter element. I generally change the Racor element every two years and the Yanmar one at twice that interval. YMMV.