Cub Cadet 7275 hard starting warm

[sidecar]

I'm having trouble starting my tractor when it's already warm from running. 1997 Cub Cadet 7275 (Mitsubishi, direct injection diesel). Owned since new, 1750 hours.
Starts right up when cold, runs and idles fine, no misfiring or stumbling when under a load. About half the time, when restarting the tractor after it has been used for a while, it will not start regardless of how long you grind on the starter, unless the throttle is opened at least 1/5 above idle. Then it starts right up and runs fine. It has ALWAYS started easily with the throttle all the way down to idle.
It's got fresh fuel, new fuel filter, cleaned fuel bowl, all fuel lines intact, no leaks at the injection pump. Any ideas on where to look next?

 

[Cub 7274]

On my 7274 it was the injection pump failing finally had a no start cost around $1300 to repair it.
Something to do with small springs inside the pump breaking worked fine after that until I sold it.
Mine had about 1100 hrs at the time of failure

 

[sidecar]

That doesn't sound good. Not looking forward to $1300+ !