Guys thank you for your advice, AV8TOR i am using the lines that comes with the engine. Viton, they hold much heat than regular neoprene, and don't have problems with my carburetor line; this line is far away from the engine's head, i think i can solve the problem by taking the pressure fitting as far as possible from the muffler, i include a picture of the project i am planing to do i'll appreciate any comments you have, unfortunately i cannot use any fuel line directly from the muffler viton, neoprene or tygon i guess the only line this muffler can handle it's like earlwb said silicone tubing, the one that we use for tune pipes but i don't know if this comes in small sizes like 1/8, thanks again guys for all your help.