Originally posted by kevink2
I've also been told some fuels will leave more of those deposits than others. I think I've had more of that black stuff running O'Donnell (pure synthetic blend) than Byron fuel types (castor plus synthetics) for example. I usually try to run around 240 to 250. I'm in the process of experimenting with some Mugen fuel because of this very "problem" and will know more after this weekend. 
Had better luck running the Mugen (Byron) fuel in regards to fuel deposits. Ran my J-Tec at 280 for a 40 min. main, and it's clean. It leaves a nastier residue on the pipe though than O'Donnell. I also had to lean the motor a bit more with the Mugen compared to O'Donnell. Little less hp but runs cleaner, me thinks.