the engines internal parts are expensive and there are many. So if a engine needs a rebuild, it's about the same cost to replace it nowadays. A new kubota engine will have all new injectors, pump, lines, starter in many cases, alternator, belt, water pump, basically it's complete enough to start/run it OFF Of the machine (not that I suggest doing that of course).
Kubota injector pumps and injectors RARELY fail without "help". In the 30 years of dealing with them, I think I replaced 1 pump and one injector because they were questionable. I have, however, had to replace many pumps because the owner/operators ran the fuel system dry, and tried to "bleed it" by "cracking the lines loose"--at the pump end. You don't need to do that, ever. That's the wrong way to bleed them and can cost you a pump. People see that stuff on TV mining shows and logging shows and assume it's the right way to do it and it's not. You don't ever bleed them at the lines on Kubota, rather at the bleeder (which apparently nobody knows about?). if you crack the lines at the pump, there is good chance that the delivery valve has been rotated, which damages it/them. That's where I have had to replace a bunch of them over the years. It is fixable but typically the shops that specialize in rebuilding the smaller zexel and bosch pumps charge really close to the same amount to rebuild as it is to just replace it with an OE Kubota replacement pump, and with less downtime.
and on kubota, one should never (EVER) spray anything down the intake while cranking the engine. That is almost a guarantee to bend one or more rods regardless of what you spray in there whether it be diesel starting fluid gasoline pee, water, beer, def, etc.
While reading the comments I noticed a lot of "diesel mechanics". Though, I haven't seen too many folks tell you to check the engine compression. I would bet that you have low compression on at least one cylinder. Most folks don't have a compression tester for kubota engines, so most folks "ASSume" it's "good". 300 psi won't run. On that engine it needs to be close to double that. At 400 they're very very weak, typically smoke until warmed up and then they're running but low on power.
The original post said low power and smoke. I'm going out on a limb and guessing that the compression is weak on one or more cylinders. The usual cause on these is overheating. Overheating also cracks the head a majority of the time. The result of low compression is that the engine might run on one or two cylinders but it's still pumping fuel into all 3, just not burning it, so that fuel is pumped into, then it's blown out (because it isn't combusted) through the exhaust system as white or sometimes almost a bluish smoke. And then--usually the "internet diesel mechanics" show up and tell you that you have a bad pump or injector, which is, again, very rare with Kubota engines. Normally it's another problem and replacing the pump/injector wasn't the only repair made, but that is never told...typical of internet forums, you never get the whole story.
