You should not have more than about 3 or so inches in front of the firewall. It is here that I use a piece of 2-56 rod threaded on at least one end for my ball link or clevis. The unthreaded end I glue into the end of the nyrod. I set this up so that not more than 1" of nyrod protruds past the front of the firewall. Inside the aircraft I do just like rcign suggested, I support the outer nyrod wherever I see that it tends to take a bend or flex. This usually solves my problem. On the end nearest the servo, I again use a piece of 2-56 rod, usually a short one threaded on both ends. This is screwed into the inner nyrod and is long enough not to allow any inner nyrod to stick out of the end of the outer nyrod.
I hope this helps, if it doesn't, e-mail me and I'll shoot you a picture.
Good luck
Make sure you don't have a bind on your bell crank if you have one on the engine and also make sure your carb butterfly moves smoothly. I've had some in the past that would bind and needed to be worked open and closed a few times to smooth it out.