1650 Hydraulic Fluid

Here is a scan of the Hydra-Lectric Stop system cover for the remotes on your tractor.
First you should have the base end of the cylinder attached to the outlet directly below the location for the restrictor as shown, you should move the lever forward to lower the cylinders.
Have you or someone had the restrictor assembly out of the cover? Perhaps some of the parts have been lost. As you can see in the drawing, as oil flows out through the interlock ball it forces the plunger back against the spring, thus nonrestricted flow during extension of the cylinders. The screw has a tapered end on it, thus as it is turned in further the opening becomes smaller. Now when oil is returning from the base end of the cylinder (interlock ball is held off it's seat by the interlock plunger) the plunger is held against the seat by the spring and flow of oil. Perhaps some material has become lodged between the plunger and seat.
You can carefully take the assembly out to check for all the parts and anything that has become lodged. Remember that there is a passage below the spring area where the connector is between the cover and base. If parts fall off, they drop down into the base cored passage. You can retrieve them by taking off the outlet pipe in the base unit and getting them with a magnet. I assumed that you have the Hydra-Lectric cover, a depth stop cover has the same restrictors, however they are both located in the rear passages in the cover.