How and when to change engine oil:

The engine wears the most during cold starts. It takes a few minutes before the oil pressure is correct in all points of the circuit.
So let your engine warm before open fully the throttle ...

These engines, in 1970, was designed by Honda for displacements of 90cm3. The head of these engines just a little more air cooled area.

Their cooling capacity is low compared to their power  (from 107 to 150cm3) and use.

The oils are degraded due to large engine temperature (above 120 °) and because they keep dust in dirt (detergent effect).

So if, in summer, you use strongly your engine, it can beinteresting to use the 100% synthetic oil and drained frequently. In recreational use there is not necessarily needed.

There is only one compartment of oil on these engines. Attention from below there is a cap slightly tilted which is the camshaft tensioner. The drain plug is on the right side.

A dirty air filter and not greased let go of the dust that will use the rings and pass into the oil.

The breather hose lets dust in the crankcase. It is prudent to mount an air filter on its end.

The 'breather kit' or 'breakdown breech' limits the upwelling of oil through the breather. This problem occurs during this extended acceleration. Including use enduro or road. You can limit the losses of oil by installing a small Uni Filter  at the front of the fuel tank to be connected to the venting free engine through a pipe from under the tank.