As to the two filters, the air filter and the PCV filter, they are supposed to be replaced with new ones at certain fixed frequency while a complete system of anticipative maintenance would stand for the timed checks on the two filters in between the changes. The air filter is positioned at the upper part of the suction housing arranged on the upper part of the engine, and it is possible to replace this filter without removing the upper plate of the air cleaner which is fixed with the help of a wing nut ; it is necessary to lift the indicated upper plate and, before doing this, to dismantle all vacuum hoses connected with this plate. It should also be noted that when removing the top plate it is easy to inadvertently drop something into the carburetor. The air filter can then be lifted out of the housing, and to know its condition put it for checking against strong light or use light on the inner side of the ring shaped filter; if light is visible through the paper element of the filter then the filter is fine and should also check it all around. The inside of air cleaner, with the aid of rag, should be cleaned, replace the old filter by putting it back at the bottom of air cleaner housing if it still has some usable life left or dispose the specified interval has elapsed put the new filter into the air cleaner housing so that it fits properly. Any vacuum hose which is disconnected should be connected to the top plate and the top plate should be screwed back with the wing nut. The PCV filter is also normally located inside the air cleaner housing; with the top plate removed, the filter is at the side of the housing; to access the filter, you just release the hose clamp at the end of the PCV line connected to the filter and detach the hose. The metal locking clip which fastens the filter holder to air cleaner housing has to be unlatched and then the filter along with the plastic holder can be withdrawn. It is necessary to unscrew the old filter from the filter assembly and take the new one to make sure that they are identical; the new filter with the metal locking clip should be placed in its right place at the air cleaner. On the PCV hose, it should be connected and clamp made around the extremity of the hose should be tightened. Last but not the least the top plate of air cleaner if removed maybe fixed back again along with any vaccum hoses that were removed. In some engines the PCV filter is not at the air cleaner, though it may be in the PCV hose; look for hose going into the side of the air cleaner housing and trace to the filter. Most 'in-line' PCV filters can be replaced by pulling a filter off the hose and pushing another one into the hose.