Worked on getting a late 9U running again this past weekend. Had been parked for about 10 under cover. Got hot the last time I was moved but I am pretty sure that was because the pony engine water pump seal failed and leaked out coolant while stored in barn.  Pony runs, main engine started fairly easy but was missing and smoked as soon as it was started.  Ran until water temp came up and water and oil stayed clean but the miss stayed.  Number two is the culprit tested by cracking the injector lines.  Went back the next day and finished servicing tractor and took it for a drive, no implements handy to load with but with brakes and some steep hills I worked it enough to clean up the wet stacking nd it got better but after idling for 15 minutes it started missing more and wet stacking again.  Has a definite pop almost like a backfire sound but not every time it should be firing. Under load it cleans up and blows steady black smoke and no noticeable misfire.  Thoughts on what to do next, I am thinking of waiting to hook it onto a cultivator on and see what happens. What would you try?  Mainly interested because it is one of the few non turboed mostly original farm cats left around here. Thanks, Mike 

Usual process is to move the injector nozzle to another cylinder and see if the problem follows.