Hard to start YSE12
Watch out for starting fluid. There is a good chance that it will break the piston. To gain the compression needed for diesel operation, the top ring groove is a little too close to the top of the piston to withstand the impact of a starting fluid explosion. The YSE engines were built from 1974 to 1976 so you have had a lot of good service. The Y series engines require very precise adjustment of the governor-throttle mechanism. The adjustment is described in the service manual. The instructions are a little hard to follow but they show you what you are trying to do. Sometimes an extra tweek is required. The best bet is to get someone who has made the adjustment sucessfully to do the job. That person should also acknowlege that the adjustment will make a great difference if done properly. I know of two new engine sales that we lost when we made the proper adjustments on Y engines for customers that had done "all they could" and had relegated their engines to anchor status. (The person described above will probably be a competent Yanmar mechanic) Hard starting can also be the result of low compression. This can be checked with a good gauge, designed to measure diesel compression. This can go above 400 PSI in a very short burst, which requires much more than the standard automotive gauge. If lack of compression is the problem, its time for a rebuild, but the adjustment above is still required. If, when removed, the pistons are cracked, the adjustment was probably the problem and the ether used to overcome did the engine in. I hope the adjustment bails you out.
