I had a problem last weekend, I was getting a bog and backfire out the pipe on hard acceleration. Motor was totally stock, only thing I did was clean the airfliter.
I thought maybe I got a speck of dirt stuck in the carb from doing the filter. anyway my friend works at a Honda shop here and he was going to put my cam pipe, and goodies on for me this weekend, so he said he would address the bog and backfire at the same time.
Long story short fellas, I had water in my gas tank and in the bowl of the carb!
He told me I had bad gas and I was like your nuts, I had a 5 gallon can and I filled mine up and my buddies 400ex at the same time, his ran fine over the weekend and mine ran like crap on Sunday, Saturday it was fine.
He right away asked me if I washed it off Saturday and I told him I did. Next he asked me how I did it, I told him I washed it off with my pressure washer and I had it on it's rear wheels with the gas shut off.
He just smiled and laughed at me. He said pull the gas cap vent hose out of the steering stem, I did, and I knew right away what happened. That hose is about 26 inches long!!!! I blew water in the tank threw the gas cap vent hose when I had it on the rear wheels. Anyway guys cut your vent hose a little shorter and pinch it off when you wash it. Why Honda left that hose that long is beyond me. Just my 2 cents and a tip from my misfortune.