Hi, I thought I would share this here in case anyone has similar problems. Bavaria 32 2005 MD2020. After I changed the pre fuel filter (CAV) as well as fine fuel filter, engine started OK and was happy running in idle and up to 2000 rpm. Going passed this point made the engine go automatically down in revs to about 1000 and then creeping up to 1500 and stay there. I suspected some air leak somewhere, so changed the o-rings on the CAV filter and refitted the fine fuel filter, to no avail. It was only after I loosened the CAV filter from the wall and turned it upside down that I saw that the bleed screw on the top was slowly dripping fuel. As the screw was already very tight I changed the sealing washer to a copper one, and fastened it again. After that the CAV filter was not leaking fuel anymore when held upside down, and the engine ran fine again, was able to rev passed 2000 rpm with no dip in rpm. So looks like the bleed screw was letting in a small bit of air even though it was very tight.
good to know. thanks - it's one of those small quirks that can be overlooked.
Well done for finding it.
You only need the tiniest bit of air getting to cause problems and it can be quite frustrating sometimes trying to find it.