Try this,
Try backing off the nuts on the retainer enough to let the injector move up a fraction of an inch and then crank the engine. The compression will loosen it and then you can take the nuts off and remove it. Just a note of caution about this, if you take the retainer off and then crank the engine you may pop the injector out with some force and that may cause problems depending on what it hits.Also try www.freeboards.net/?mforum=yanmarhelp if you need more help.All the best,Robert Gainer