[overbored]

Had a similar problem a few years ago on my previous boat, tried everything on the injector timing. bought a new pump because it cost less the they wanted to rebuild. kept removing shims until it was in time and ended up with no shims. by that time i was tired of testing and just left it and it ran good. asked the mechanic at the Yanmar dealer and he did not know why but said he has had a few others that way.