In a nut shell yes. But the difference in timing is very minicule. the air gap can effect the spark strength more so. Ran across a engine that said the gap was .008-.016 but found that it would only run and start correctly when set at .010 .
match book cover is about the right thickness. the engine I discussed was a mtd (chineses engine) push mower with electric start that wouldn't start with electric but would with the rope. Briggs calls for a gap of .010-.014. tecumseh is .0125
Yep, a matchbook or business card is kind of a generally accepted feeler gauge.:biggrin: They don't rust, and you can usually find one quickly, unlike all the other measuring devices in my shop...:ashamed: