Check to make sure that the IAB (Intake Air Bypass) mechanism is working.
Sitting in front of the HP fuel filter you will see the IAB control diaphragm. Disconnect the vacuum hose to the diaphragm. The diaphragm is held in place by two Phillips head screws that you typically remove to get to the HP fuel filter. Remove those two screws, swinging the diaphragm aside. Grab the lever coming out of the diaphragm and pull on it as if the diaphragm was being activated. It should move until the spring arm engages (or nearly engages) the “stop” adjustment screw. Then let go and it should pop right back in place. If so, the IAB is operating as intended.
If you can’t move it, or if it does not pop right back in place, then you need to remove the IAB and clean and lubricate the shaft to the IAB bevels. Note that apparently Honda does not consider this a serviceable item, so from here on, you are on your own. The worst case scenario is that you cannot fix it and will need to fork out about $343 to get a new one from
www.boats.net. Part number 17130-ZY3-003ZA.
Before you re-install the diaphragm, hold it in your hand, gently push the arm back into the diaphragm, and hold your finger over the opening in the tube that the vacuum hose attaches too. When you let go of the arm, it should come out a little bit and stay there until you remove your finger. If so, then the diaphragm is operating correctly. If not, the diaphragm is leaking air and must be replaced. Unfortunately, it looks like a replacement is not available, since that diaphragm is part of the entire IAB assembly. However, I suspect that if you search around a bit, you should be able to find a replacement for this fairly standard part.
Also, if you have access to a good hardware store, it would be a good idea to replace those two metric-threaded Phillips head screws with matching hex head screws. It will make it a lot easier to remove them the next time you change out the high pressure fuel filter.