yanmar yse12 fuel pump?

I have a problem with the regulator on my fuel pump, i removed and dismantled it because the pump would not pump fuel and i have no idea what position the spindle needs to be in, from what i have read in your articles it would seem this is quite critical, i have already replaced the plunger and delivery valve spring and checked the cam, also it would seem that it is trying to pump the fuel back up the fuel pipe!
Any help would be appreciated.

keith
August 2011