White Smoke from Exhaust 6341 Super

I have a Zetor 6341 Super. It just started puffing white smoke from the exhaust. Any suggestions before I get started diagnosing? Thanks.

White smoke is usually caused by either water or coolant in your cylinders being burnt and is steam coming out the exhaust.

Thanks, diyfarmer. I have lost no coolant at all. The smoke smells like diesel, which is leading me to believe that it's unburned fuel.
I haven't had time to start work on it, but think I'll pull the injectors and see if they are corroded first. If it smoked all the time, I could disconnect the supply line to the injectors one at a time until the smoke quit. But it only does it after it has idled for a few minutes or when it first goes into a load.

I did a little more investigating and found that it was not "white smoke", but "blue smoke" - and maybe a little of both. I had to get in the barn and close the big door to find out. My eyes are getting a little age on them...
So afterwards I removed the air filters and cleaned them both. After installing the inner filter, I started the engine and heard what sounded to be a "sucking" noise. I think I may have a valve either stuck or burned. Maybe a valve seal leaking by.
Any tricks to that part before I start digging deeper?

Thanks.

Have you changed the engine oil in it lately ?

Yes I changed the oil about 100 hours ago.
I decided to back the tractor into the pond with the shredder attached and running to put a load on the engine. It helped a little but still smoking.