Normally it'll be easy because fuel is spilling everywhere. These regulators are very simple, it's just a spring and a diaphragm which works as a bypass valve and there really isn't anything to fail. If it was working properly, it should stay that way until the diaphragm fails and a leak happens or the spring rusts enough to lose it's tension. The only problems I've ever seen are leaks, anything else is a pump or line problem.