This is basic but essential….
Couple of seasons ago, I had several instances of air lock problems with my Yanmar 2GM, resulting in the engine cutting out. There is nothing quite like your engine cutting out to undermine the confidence of everyone on board! We try to do as much under sail as we can – picking up moorings and coming alongside when conditions suit – it is good practice for situations where you can not fire up the engine for whatever reason.
In every case of Mr Yanmar cutting out, the single cause was dirt in the fuel tank clogging the system. Every inboard engine should have a primary fuel filter located on the fuel inlet line from fuel tank to engine. The filter needs to be changed regularly – at least once a season and otherwise as required. When I changed the primary fuel filter in the situation described above, I noticed it was quite dirty. I also examined the secondary filter located on the engine block and found this less susceptible to dirt, possibly because the primary filter is effective. I gave the fuel tank a complete clean and spent a few bob on a good fuel funnel. The funnel I had prior to this had a coarse filter mesh and was pretty useless in removing contaminants. This one does the job properly.
Everything that goes into the fuel tank passess through this funnel at least once. Never had an airlock in the two seasons since. It is an eyeopener to see the amount of contaminants held on the filter. I have added a job to my winter mantenance list – drain down the fuel tank completely and give it a good clean out. Funnel stays in the stern locker and is available when fuel top up is required. And I try to carry a new fuel filter on board as a back-up.