I seam to have a similar problem with my 31 year old Yanmar 2gm 13hp 3400 continuous HP rated engine.
I Was having some problem at low rpmís so, I naturally went to change the fuel filter, the one that is part of the engine. Anyway It cranked up but now runs very poorly. I have heavy black smoke suit on the water. Seams like dry oily stuff.
I think $230. for new injectors would fix part of the problemof being old and never serviced, But what could Iíve have done to cause the heave black smoke from todayís filter change? It only got real bad after I changed the filter?
Thanks for your help
Black smoke is an indication of fuel that is not being burned, it can be from poorly maintained injectors, a fuel pump that is not timed right, or a restricted air flow. I would say that what may be happening, and this is just a guess, is that the previous filter was restricted a bit, and it lowered the pressure of the fuel at the injectors just a smidge and now it has some build up on the injector nozzles. You can remove the injectors and check the spray pattern to see if it is a cone shaped pattern, and tell if that is what is going on, or you can go the route I suggested with the OP and run it with the fuel polisher and injector cleaner from a clean gerry can. Personally, I would try that first, and if it does not clear it up I would pull the injectors.
The great thing about these little Yanmars is that they have a super easy to replace injector, and if you are handy at all you can do it yourself, providing you have the tools. The manual is here, http://j30.us/files/yanmar-manual.pdf
and it will show you some of the procedures to follow in maintenance and it does show how to check the injectors and timing. If you are not comfortable in doing that, then you will have to take it in to the shop. The timing, and the injector spray pattern are critical, and if one of those is out, or you are not getting good airflow it will run rich and smoke a lot.
So, check to make sure your air filter is clean. Check to make sure you are getting clean fuel all the way from the tank to the injectors. Check the timing and the spray pattern and it will be somewhere in that list. My first guess is that you just need to run the fuel polishing and injector cleaner, and it will probably clear up, it is possible that when you changed the filter it dislodged some gunk and you are now dealing with that at the injector tips.
PM me and I will try to help you if I can.