Last summer (2013) my zd18 would not start without pushing throttle about halfway forward. This year I have had to keep moving the throttle forward to wide open to get it to start. Once started it runs great and when shut off it will restart no problem. The other day I cranked it several times with throttle open and it would not start. It finally started and I ran it for 2 hrs with no problem. Ive changed the two cartridge fuel filters a couple of times over the years. It has 820 hrs on it. I'm not much of a diesel mechanic and don't want to pay a mechanic if I can fix this myself. The mower is a 2002model. Thanks