Returnless fuel filter replacement

I have a 2006 Carver 33 SS with Crusader 6.0 l gas engines installed. I am planning to replace my fuel filters. My port engine rpm's are cycling up and down, up to 300 rpm's when I accelerate from 1000 rpm's to 2500 while underway. Once I reach 2500 the problem seems to "go away". In neutral, I don't have the same problem. I have read in other forums that the filters may need changing. If anyone here has other ideas or thoughts on the problem I would appreciate it.

I have studied how to change both the pre-filter and the water separator filter in the Crusader manuals. I have a returnless system with a Racor 110 AT separator which uses a Crusader 47047 filter. I feel pretty comfortable changing the filters except for one issue I can't seem to get an answer for. I traced the fuel supply line back to the tank. I don't see a manual fuel shutoff valve anywhere. Perhaps I am missing it, but in reading some forums, the answers aren't clear. Is there something I need to do to keep the fuel from siphoning out?

Before I install the filters, is there anyone here who could help me with this question?

Thanks!

Nate

Thanks. It had an anti-siphon valve on it. Was able to get them changed out.