Abu, Since most of my engines are rear carb gassers now, you generally have very limited access to the needle screws. What I am doing on most of my models, is running small tubes, very well supported, right up to the needle screws. I bought a long, thin screwdriver that fits in the tubes and is guided right onto the head. All of this needs to be done quite accurately. I use 2 tubes, one for the low end, and one for the high end. THis will all depend on your carb, but I am sure you can make something like this work. Even if this tube has to be run thru your former.