Tractor Repair: massey fergusion tractor, engine, timing

Question
I bought a massey Ferguson 1990 4wd 390 agricultural tractor a couple of years ago
it is very hard to start in cold weather
i have replaced the following
fuel lift pump , starter motor , new battery,and glow plugs and all filters and cleaned out fuel tank
i also took the injectors and injector pump off and got them reconditioned
i marked the pump prior to removal and upon reinstalling aligned my marks and refitted the pump
immediately i had more power but it is still hard to start in cold weather
when hot it fires up within 2-3 turns (effortlessly)
when cold you have to glow for up to 60 seconds and turn it over 20+ times before it will fire up and this is not normal of a perkins engine
i have a suspicion the pump was taken off prior to my ownership and the timing could be out does anybody have any suggestions
just a couple of points to note when the engine starts there is a lot of black smoke and it also sounds a bit rough not a typical perkins sound
when it warms up the noise settles down and the exhaust has a blue type color to the fumes
the tractor uses a little bit of oil but nothing to be concerned about approx 1 liter for 60- 100 hours work depending on work load
we have another Ferguson and 1 touch and it fires up every time and this is a old jalopy

i would be grateful for any suggestions
regards
vince cunningham

Answer
if you have marks on the injector pump you can change the timing slightly by turning the injector pump shaft anti-clockwise within the gear(this is as you look at the front of the engine) a small bit this will retard the timing slightly and should make it easier to start.try this(you might need to try a few different positions)
but your problem could well be worn rings and a build up of carbon on the pistons and and the valves so if altering the timing doesn't help id get new piston rings and re-grind the valves in the head and obviously return the timing to the original mark
if this is the engine with the 4 bolts on the injector pump shaft flange changing the timing should be easy enough some pumps have elongated holes in the injector pump mounting if its this type you can retard the timing by loosening the bolts and moving the top of the pump away from the engine