Most modern cars built in the last 10 years require SAE 5w20. But some do require other weights. Refer to your owners manual for the correct weight for your engine. Do not use anything else.
Of course you can. A small 4 cycle engine uses the exact same oil as used in any car.
10W-30
regular 10w 30 motor oil
10w 40 wet clutch oil.
It depends on what kind of car we are talking about. Check the oil cap or owners manual for your cars recommendation.
10w-30
10w 30
10w-30
10w-40
10W 40W 4 Stroke Motor Oil
10W/30
10W-30