I have an 8.5hp Briggs that will let out a good bit of white/blue smoke when started. It only does this on occasion. For example today I started it & loaded it on the trailer, no smoke, when I started it at my first account (about 6 blocks away) it put out a big puff of smoke & then cleared up. I had thought about water in the fuel but, I am using the same gas in my Kolher, without smoke. The only change I have made is I started using synthetic oil. Any ideas????