Lots of people are taught that you need a smoke trail or its running lean. To me it means my plug is too hot. Switch back to a hotter plug and you will see that you will have to richen the mixture, but the RPM may be down. Your smoke trail will return. But I assume you put in the colder plug because of high nitro, so you may as well get used to no or little smoke trail. Some synthetic oils also leave less smoke.