My john deere 1070 loads up under a load and will stall. I changed fuel filter which was loaded with "gunk" and it ran ok for a while then is doing it again.

Time for a valve lash adjustment.

smokes under load bad rings

Is your "load " in a bind of sorts with engine reved up when you engage it? check the load. something may be stuck.

John:

The puffs of smoke when you put the machine under a load make me think that your carburetor is loading up and needs to be adjusted. Adjust the fuel/air adjustment screws on the carb until it runs properly.

Have you checked the fuel pickup in the tank for blockage?

When it runs rough is it blowing dark smoke? This is a sign of running rich like a choke will do and can cause stalling especially when the motor is warmed up. If it is not blowing dark smoke it sounds like maybe your injectors are not working properly and it is not getting enough fuel through them under load. either way as an injected machine it sounds like injectors may be the culprit since youve taken care of some other issues. You might try running a heavy dose of an injector cleaner through it (I've had good results with lucas brand) and see if that helps. Otherwise, you might try to manually clean the injectors.

you could have a weak coil and misfiring under a load each cylinder has it own coil on that engine you can get a inline spark tester to see

Check your arrow on your filter. Arrow to carb,

back firing???? out the exhaust or the carb.
my first guess is the spark plug wires;(under load). any thing in the ignition system; plug too.
back fires out the exhaust under load sounds like low fuel... rebuild carb or star by cleaning the fuel filters.

The lookup at:
http://jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.HomePageServlet_Alt

for the model 1070 harvester shows it is a 3 cylinder unit.
What I might recommend is pull off the valve cover and make sure the intake valve is moving up and down as the engine is cranking. (dont get cut up)
It sounds like a pushrod may have fallen out.
good luck.
Joe