MF150 suddenly hard to start

I've had my 150 diesel for about 2 years now. The entire time, it's been very easy to start, even in the cold, turn the key over, and it fires right up (may take a few seconds in the winter). About a month ago, it got really, really hard to start, even with the air temperature is in the 70s or 80s. Additionally, its smoking a lot (black) under load, more than I remember in the last few years. This morning on start, it was a very light gray/white smoke.

On top of that, it sure feels like it's down on power, as it doesn't want to run my flail mower like it used to.

Knowing enough to be dangerous and that's it, I'm inclined to thin it's either a injection pump issue, or a head gasket (both?). Any one else want to take a guess. I bought the tractor with a stuck hour meter, but it was at 5000 the last time it worked, so who knows what the actual hours on it are.
 
I would start with the basics as mentioned if they have not been done in a while- air filter, fuel filters, oil change even. Black smoke usually means to much fuel. It could be a lot of things, but most likely not getting enough air is the problem. Check the whole intake path too.
 
(quoted from post at 15:33:26 09/25/20) Have you replaced your fuel filters? If not give that a try.

Fuel filters were replaced last year, tractor has probably 50 hours or less on it since then. I pulled the air filters out yesterday, they were more or less clean, nothing on them.

I'll have to grab another fuel filter and replace them again, I know the first time I replaced them on this tractor, they were rock hard and weighed a ton, totally full of rust and sediment.

I have been watching the coolant level, and it hasn't really dropped at all, which leads me away from thinking it's a head gasket.
 
It might be worth checking the valve clearance. With that many hours who knows when they were last checked. A valve stuck open could cause the problem. I had a similar situation with a 165 with an intake so far out of adjustment that it smoked and had little power. It was fine and then quite suddenly the problem appeared.
 
Changed the fuel filter out today, and pulled the air intake apart, just to check for blockage. No blockage or anything was noted.

I do know that when this first started, I may have left the fuel shutoff knob in the shutoff position for a few weeks while I didn't use the tractor. Seems like that could be part of the issue.

Either way, further work on the tractor will have to happen in the winter.
 

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