You got some pretty smart guys out on this one. If I may, one problem I had with Honda's is the float bowls on the carbs have a tiny port made into them that goes across the bottom to a small chamber on the side of the bowl. This port is very difficult to clean out if it gets clogged and if this is the case the bowl may even need to be replaced. I think they're $90. Honda carbs are very complicated and must be in top condition as is the case with all carbed 4-strokes but seems more so with a Honda. They must be accurately synchronized as well, this can not be done by ear or eye. I have to admit, of all the different engines I repair, Honda's are the most difficult in that they are so sensitive to any type of abnormality and they are unique in construction. Your marina may be right but before I started throwing money and parts at it I would want to hear some logical explanation. How did he come to this conclusion, is he sure how to fix it, and what if it does'nt, then what? It may still be the carbs, I've cleaned them twice before to be sure.