Make high voltage spark travel further?
If I add a length of wire the spark becomes very small.


Is the wire coaxial (like a cable TV wire), paired (like speaker wire), or a single-conductor wire with the current returning through a ground plane (standard grill-igniter setup)?

If your answer is option #1 or #2, then you're probably losing energy to insulation breakdown/arcing, or capacitive transfer. However, if it's #3, then that would change the "usual suspects" we'd need to look at to find what's going wrong.


  If not could I use a spark plug or something and make a simple circuit with common electric components?


Depending on your intent, expertise, and available parts, you could make a flyback-transformer circuit to send a spark (pretty much exactly how an automotive ignition coil+spark plug functions).