I had this problem on my 2002 recently and had to check my
fuel line. Luckily I had a
electric portable
fuel pump and opened the bleed nut on the secondary filter and pumped
diesel through from a Jerry can . The
engine ran beautiful no missing or reduction in revs even on tick over which showed that I had a problem fro the feed to the secondary filter and followed the line back through the
pump ,primary filter and
fuel tank. I thought at first it was dirt in the system but then read up on the
Penta Engines. They are very susceptible to air leak problems air being sucked in with the
fuel and when it reaches the carburettor the air causes a drop in revs. I also noticed that when the second filter was primed and full air bubbles were continually coming out of the bleed screw this told me the problem was upstream. All I can suggest is that you put what we in the UK call plumbers tape round all the threads on your fuel connections where you can from the secondary filter to the
fuel tank. Tighten the unions and hopefully you should solve the problem. It worked with me. If your
engine has a mechanical
fuel pump the
diaphragm might be damaged and sucking in air in to.