I went from 280 to 320 jets. I really opened up the exaust though. After I opened it up. I spent most time on the exaust itself. Hand sanding with siiconcarbide paper (wet sanding) up to 280. Then I used black scotchbrite on a dremmel cut off wheel. Went through about 2-3 felt wheels with green rouge came out with a mirror polish. Any time I take the exaust off I look in port and its clean and smooth. No build up. Seems like when there is imperfections build up occurs