What are the three gaps in the ignition system of gasoline engine? What's the difference between being too big and too small? How to adjust them?

Three clearances: flywheel and magneto clearance, spark plug clearance and valve clearance. Too big or too small can be inverted: gasoline engine is difficult to start, it can't start, and the power can't add up. Generally, the flywheel clearance is 0.3-0.4, the spark plug clearance is 0.6-0.7, the valve clearance is 0. 1-0. 15, and the exhaust valve is slightly larger. The above experience is summarized for your reference.