This video is a quick run-through on how to synchronize your GL1500 Honda Goldwing carburetors for years 1988 to 2000. The 88 model has a fitting on each side of the manifold to connect the Vacuum gauges to. On newer models, you will have to purchase or make a connector for one side to be able to connect the gauges to. To stop the needle from jumping and get an accurate reading you can either purchase a valve to close up the vacuum line going into the gauge just enough where its still moves but not jump or just pinch the line until it stops jumping but not enough to where its blocking all the vacuum pressure. The gauges were purchased from Harbor Freight for under $15 each.
Vacuum Tester
https://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html