Check your compression. Clean your carbs? New spark plug wire end caps. Need new needle and seats? Primer may not be any good. If it has a choke, take the choke plunger assy inside the carb apart and clean the corrosion and make sure the it's adjusted properly so the plunger is seated. Try BR9EYA plugs. Not running some old gas? Moisture in the gas? Too much gas or not enough?