Re: what did you do to your motorized bicycle today?
I ordered a crankcase oil breather assembly to see if my 5 years ago refurbished Briggs 4 stroke 3hp engine has less smoke out the muffler. Its not much, but I expect it could be better. There has been very little run time on the engine till now. It had the valves and seats cut and length of the valve compensated. The rings also replaced, so it has good compression and starts right up no problem.
I know the older cast iron engines have parts that are not in a crimped metal case. With those you can see the spring inside and replace it with another new one I'd bet. Those type there is no return tube to the air-filter / carburetor. They just vent the oil mist down the side of the engine.
This 70's era 80202-0430 aluminum Briggs engine, you have to replace the whole breather. I have a couple of extra air-filters that I will install if I see that the one in there now got mucked up from the worn breather spring not working properly and the return tube sprayed a lot of oil mist on the filter.