I have experienced some servo jitter when using piano wire for pull/pull. That is with a servo with all metal gear train. SO I use Kevlar. You can buy a spool of it from your hobby shop. Get the kind the control line guys use. It will last a long time. Kevlar seems to be the most resilant to temp changes and doesnt stretch. Very tough stuff. On the part of the line that is exposed at the back of the fuse to fuel exhaust... just a drop of thin C/a on it and it will be protected. Its also very easy to replace a line if needed even at the field. Use eyelets at each end and tie off the line with a double knot and a drop of C/A on the knot and it will not come loose.