It's a device Honda designed to bleed off some compression at cranking speeds, to make the engine spin faster with the starter. It's supposed to disengage by the time the engine is spinning idle RPM (so setting idle to spec could actually help if it is idling too low). Sounds like you've been that route already tho. It consists of a mystery thing that's pressed on the cam (you'll know it when you see it) and a small pin and spring that rest in the head and help the mystery thing do it's job somehow. If it sounds like I don't understand EXACTLY how it works, it's cause I don't. A lot of people at Honda tech services don't either, LOL. I worked on one 400ex that the customer said was starting very hard. When I turned it over, it sounded bad, in fact I assumed there was top end damage and stripped the top end. I found no damage at all. The problem turned out to be the decomp, and Honda tech told me to replace it, the spring and pin too. There was no apparent way of telling the old one was bad by looking at it. Anyway, the decomp doesn't work with aftermarket cams for the most part, so there's a lot of people out there running without one. I also personally know of one person who is running the stock cam without it, to no apparent disaster yet. I guess if the problem persists after several rides, it's probably not going to get any better.