I have a Yanmar 155D that I use for tilling my garden. Last couple of years it has progressively weakened and now it is very hard to even get it started. I am going to do some checks on it and see if maybe it has a plugged injector but I believe it has a bad cylinder. I have to run it up to 3000 rpm just to move it and when I till it spews black smoke. Meaning it has unburnt fuel which leads me to believe it's a bad cylinder not an injector. It has over 1000 hours on it so probably due for an overhaul anway. One other thing I noticed, when I pulled the air cleaner there was a bunch of diesel in the bottom of the cap. Not supposed to be there........