Appreciate some advice. Currently in Howth on my way back to the Clyde. Engine has been fine all trip but last couple of days has developed an apparent fault. Engine starts and generally runs well but occasionally the revs reduce to tick over for about 20 secs or so and then recover. Happens randomly but could be once an hour or maybe slightly more often. Engine has not stalled and otherwise appears Ok. I did change both fuel filters (Cav and Yanmar fine engine filter) about 20 engine hours ago. It is the intermittent nature of the problem that has me perplexed. Grateful for checklist to work through.