Beware "generic" or "adjustable" units on the market. This Genuine Suzuki part is designed to function correctly for your Samurai.
Believe it or not, most Suzuki Samurai's on the road these days have a bad vacuum advance unit!
Per the Suzuki Factory Service Manual: "Disconnect vacuum hose from vacuum hose 3 way joint, and connect vacuum pump gauge to its hose. Apply vacuum (about 400 mmHg). And then with pump stopped, check to ensure that vacuum pump gauge indicator remains at the same level, and release it. Check that generator base plate with generator moves smoothly. If plate does not move smoothly, replace defective parts."
(that means replace this part)