It is very common for the pickup lines that feed those pump designs to dissolve. The pumps (aside from o-rings) generally are bullet proof. I haven't been into a 650, but have replaced many lines on other vl/evl saws. There should be a nipple or barb fitting at the case where the pump is located. It should route out to the tank wher the strainer/pickup is. Make sure that line is sound. If it is dissolved or broken in the tank, it should still pull oil provided you have the tank filled up past that point. That would at least confirm the pump is operating. As well, the nut on the pump and case were often punched with corresponding marks to indicate the ideal point to thread the pump body into the case. Generally when the pump is seated completely down, it will pump max volume when backed out 2/3-3/4 turn give or take. From there, the pump should decrease flow when opened another 3/4 turn or so. Set your stop accordingly to limit the pump being adjusted within those parameters. You can also visually inspect oil flow at the bar pad and set the stop that way.
