Fuel starvation problems; a long story
Terry, our 1991 Legend 43 also has a 4JH2 series Yanmar with a long history of fuel starvation, making it difficult to run at higher RPMs, particularly if the fuel tank was less than full and/or the fuel filters were starting to get a little dirty. In the first few years we struggled mightily with that problem but got some relief by upgrading to a higher flow (20 gph) 220 series Racor pre-filter. However, the problem would still rear its ugly head from time to time. Finally, last year we decided to go to the 500 GFS turbine series, not only because of the higher flow rating (60 gph) and, thus, lower resistance but also because of the much lower replacement element cost (the price of the Racor 500 elements is only 1/3 of that of the 200 spin-on elements). While installing the new 500 GFS turbine filter housings (we installed two of these in parallel, using 3-way valves to enable rapid switching underway) the local engine mechanic noticed that the long feeder tube running from the stern-mounted tank to the engine with relatively little drop only had a 1/4" ID and thus made a poor match with the 500 series filters. He replaced it with a 1/2 " ID tube (hope I got all the dimensions right as I am only working from memory) and -- PRONTO -- our 12-year old fuel starvation problem was solved. In fact, we sailed and motored the whole season on a single 500 filter without any signs of fuel starvation.Note that we always use a special fuel pressure gauge to monitor the pressure drop across the filter. In the past, however, we already would get fuel starvation problems beofre the pressure drop across the filter went into the yellow warning zone on the gauge.An alternative, which I have often considered, but never quite found the time and space to install, is a so-called "day tank" mounted directly above the engine, thereby providing a much better gravity feed configuration with a very short feeder tube connection.Hope this may give you some more things to try.Success!Flying Dutchman