Need to know the weight of the motor oil

SOURCE: Engine starts but won't stay running

an easy way to know that is to start engine and give it a shot of starting fluid ,if you can keep it running by this method I would replace diaphragm.

SOURCE: What engine oil is recommended for the Intek 24 hp

multi-grade will be fine it realy dont need a pricy oil in it this kind of engine will run on dirty cooking oil,,with or with out the chips still in it?

SOURCE: Have a Yard Machine riding mower with 21hp Briggs

It depends on the model but most riders have the following;
1. Seat switch
2. Brake pedal switch
3. PTO switch
4. Neutral switch (if its a shift model)

All need to be closed in order to start engine.

SOURCE: what type of oil do i use in my briggs stratton

You should be safe with a 10w-30 weight any major brand oil.

SOURCE: Briggs & Stratton Vertical OHV Engine 18 hp

Check your oil.

If it is overfilled, milky, or smells like gas. Your going to need to change that ASAP. It sounds like the float has stuck in the past or is still sticking, and it has flooded the crankcase with gas, which has mixed with the oil. And because it is overfilled it comes through the breather hose into the carb. This also explains the smoke most probably because the oil is spewing in the carb through the breather and being burned.