I have a 1988 7120 tractor with less than 500 hrs on a reman motor. I bought it with the reman so don't know about pump or injectors. The tractor will not start under 35 degrees without being plugged in. My grandpa has 2 7120 tractors and one will start at 10 degrees no problem, the other at about 25 degrees. Even at 40 degrees or so I have to put the throttle all the way forward and crank for 10 seconds or so. A buddy and I advanced the timing a little but it didn't help might even be worse. Tractor seems to run fine except the egts run at halfway up on the gauge just driving down the road and at 3/4 when pulling in the field. It does have the old cast iron exhaust and it still has a muffler.
It used to run a little warm on the coolant temp but I replaced the sending unit, thermostats, put a manual gauge on, and cleaned the radiator out. Now it run cool no matter how hard you pull it.