If a 1983 Suzuki 125 quad has gasoline and spark at the plug why wont it start?

Check that your air filter is clean and the air-box is not obstructed. Check the 'choke' mechanism is operating. Are you sure that fuel is actually reaching the spark... Is there a strong smell of petrol/gasoline after you've been trying to start her up? If not then you might check that the fuel lines and fuel filter is clear and that any vent in the fuel filler cap is clear too. You may also use some spray carburettor cleaner to help ensure the jets and internals are clean inside. After cleaning and checking these, items you can resort to some brand of 'easy-start' usually in an aerosol (highly inflammable stuff) and follow the instructions, taking proper care as you always should whenever fuel and sparks come together! These are all basic steps to help cure your starting problem... Engine timing, dirt in the valves, split vacuum hoses, clogged breather hoses or even a partially blocked exhust pipe will all contribute to difficult starting. Best of luck and send another question in if your successful or not! Regards from the UK