I bought a ZD21 about a year ago and have a lot of troubles with it starting. It needed a new starter and Battery and I have replaced both of them. The mower seems to not want to start with the throttle at an idle, but it will Start with the throttle turned up to full throttle. Battery voltage at the starter while cranking is 8-9 Volts. I have verified that the fuel shutoff solenoid is not sticking. I have verified that the fuel pump is pumping with the key in the on position. I have checked the resistance on the glow plugs and they are at about 1 ohm. With the temperature at 72 deg F this evening, the mower wouldn't start without turning on the glow plugs for 15 seconds and even then it died with the throttle at an idle and had to be started with the throttle turned up. The mower has less than 1000 Hrs and was previously owned by a homeowner. Thanks in Advance.