Well if you think about it the inlet is served by a single carburettor positioned centrally on the cylinder head whilst there are two exhaust outlets located front and back of the head so the two inner valves are the inlet valves and the outer ones serve the exhaust. Sounds like you might be working without any sort of manual so another tip is think of the valves as numbered 1 to 4 from front to back. Then apply the rule of five. When rocker no 1 is fully depressed you adjust number 4, no 2 depressed adjust no 3 and so on.