no filter, and I havent changed the lines, just checked them. If I were to use a filter, would that help the fuel accumulate on the carb side, and minimize bubbles getting to the carb? I know my fuel lid closes tightly, I checked the seal, and I give it a firm push (not hard) after adding fuel, or on initial fill up. I got the Syclone from Xenonproject.com,(ya ya, I know, should have gotten it from Eddie, but I didnt know of www.himotoracingusa.com at the time of purchase) so if something is defective, I'm kinda S.O.L. on warranted replacement. Initially, Ijust thought Iwas incapable of tuning a nitro engine, and Ithought that maybe the bubbles were normal...god it sucks to be a noob...