We had a similar experience with a Yanmar
4JH3HTE -- we had a Webasto heater installed and the installers cut into the plastic fuel tank
that clogged the inlet for the fuel system. Beneteau
put a very small fuel inlet hose into the tank -- perhaps 3 or 4mm in diameter. I had a new one made that's about 10mm across -- and after removing the fuel tanks
and emptying them through a baja
filter, got most of the plastic bits out. After that the fuel inlet we had made sucked up the plastic shards through the pipe and into the Racor filter. About a year later the Racor filter eventually clogged (not the filter but the actual mechanism that the filter fits into) some of the internal parts
& I had to dismantle it as well. about a 1/2 hour of re&re and a half hour of cleaning
with some compressed air and we were good as new.
The symptoms manifested themselves as a slight "cough" and loss of RPMs under load. Once I made the fuel pipe bigger we've had no problems -- other than the slight clogging of the Racor -- which I should probably put on my annual preventive maintenance
list come to think about it.
of thumb I would check to make sure that the fuel is getting to the engine true -- without air -- might be a crack in an older fuel hose letting in air. If this appears to be OK and after replacing the primary and secondary filters you still have the same problem -- then go to the back ... check out the exhaust
and make sure that it's clear ... if that's OK then you should probably call a mechanic
and get some serious help.