-To adjust the linkage just turn the screws that are on the links, you will see as it falls apart when you loosen one.
Update 4/8/2021 - I also want to stress the importance of setting the carb floats correctly.
This video shows a simple way to check your outboard carburetor links and make sure the air intake valves are opening at the same time and to full open position. This small misalignment can cause the engine to shake quite a bit especially at slow speed / idle.
Troubleshoot Outboard carburetor links and check air intake valves to make sure they are opening at the same time and to full open position during WOT.
Throttle plate sync.