I can tell you this much, I had a 420 with an Onan that had been "Worked" on by the PO and he had the wrong length governor rod on the carb. No matter how much I played with it, I could not get the governor to work. Boomer sold me the correct length rod and that solved the problem. One thing I found out on the Onan is that there is a preload on the rod. It is not just an A to B type length. The preload is what makes the governor respond at the correct time. Research it and find out the correct length rod. I used coat hanger wire and made different lengths and realized that length was the critical factor. There is a guy I know who is trying to sell two 400's and he might be able to tell you the correct length on his 400. If you PM me I will give you his number.