Bruce,
The one's I work on are a couple of years older but I think they are the same.
If, when you say, "fuel mixing chamber", you are talking about a rubberized, black, small tank like looking thing, attached at the oil dipstick tube, then I would be very interested in the recall you mention.
The local Honda dealer has told me about a recall on that device but he can't seem to (or won't) obtain any info about performing it. My shop manual calls it a "fuel chamber" but I find water in those frequently. They seem to act as a fuel/water separator. It's one of the first things I address when I get a stalling problem on one of the small rental fleet I maintain. I have learned to take it off and shake every last drop of fluid out of it before proceeding.
The sad thing is though, when I find water in those, the carburetor usually needs to be cleaned too. They are pretty simple but you really need to understand that there are a couple of things you will want on hand before beginning.
I agree that you should get the shop manual but it doesn't tell the whole story about cleaning those carbs. You will need a new idle mixture set screw if you want to clean out that passage as you are forced to break the old one to remove it. You will also want to replace the tiny O-ring at the top of the "jet set" tube as they cause problems if they don't seal. I usually just replace that tube as it isn't all that expensive and it comes with the new oring.
If you have an accelerator pump, (I'm not sure which all models do) replace that piston and spring too. If the bore that the accellerator pump fits into is gouged up or if the check ball at the inlet to the accellerator pump charging port has come loose, I advise replacing the float chamber.
Here's where I have to tell you that I work on 8hp and 20hp and the carburetors look identical. I'm sure yours looks like those too. One problem I've run into is that Honda doesn't list an accelerator pump for the 8hp but mine have them. The only difference between the 8 and the 20 accelerator pump seems to be the length of the pushrod. I have resorted to ordering 20hp accelerator pump kits and cutting the pushrod down or just re-using the old one. I don't know if that will be a problem for you or if you might have a more competent parts guy than I do.
(Can you shed any light on this Mike??)
The accelerator pump circuit on these is critical to proper runability. The passages at the bottom of the float chamber (or bowl) are also critical and are prone to clogging up. I even had a new float chamber right out of the package drive me crazy when it had a small piece of debris stuck in the vacume break passage at the bottom of the bowl. flush those "hallways" out with WD-40 with a straw in the spray tip.
While you have the bowl off, study the accelerator pump circuit until you locate the passage in the main body of the carb that is fed when the pump is actuated. It leads to a small brass tube that extends into the front of the venturi air passage (or "throat) of the carb. use a can of WD-40 or carb cleaner with it's little red straw to make sure that gas will squirt out of that tube. I prop the throttle plate open with a pocket screwdriver in the linkage arm so that I can clean that tube. When you spray into the passage, the liquid should shoot out of there and travel a good three to four feet out the back of the carb. Careful! Don't spray yourself or your neighbor's Corvette! If it doesn't shoot out of there across the driveway, you need to "back flush" it by inserting the plastic straw on the can into the carb throat, past the throttle plate, and carefully spray into that tiny little orifice in the end of that little brass tube. It can take several trys but usually works great. I haven't had one yet that I couldn't unclog but I know that if I do, I will probably need to replace the carb. Those engines will not run well if that passage is clogged.
Those little fuel filters don't have anything in them but a relatively course little screen. Like you, I was surprised when I took one out and cut it open to see that it doesn't seem to really capture anything. Just there for the big stuff I guess.
If you get her running sweet again, I strongly suggest that you drain the carb each and every trip and pull that "fuel chamber" every now and again and shake it dry. Water minerals that drop out of solution and get stuck in the passages is the bane of these carbs.
Good luck and tell me all you know about that recall if you will.