burning a lot of fuel Options

[jsf322]

I've had my 914 now since mid January and I am just about through the second tank of gas. I put 126 miles on the car and I am down to just over 1/4 tank of fuel left. I did a quick 30 mile run on a full tank and refilled and found the car to be getting about 20mpg. It is a 1976 2.0 without an air pump or cat and just under 44K miles on the car. It has new plugs, wires, cap, and rotor. The plugs were black like it is running rich and it smells rich when it first starts. Also starting it is a little trouble. It starts right away, but stalls twice and then on the third try it will keep running if I keep the RPMs up for about 5-10 seconds and then let it idle. Idle is usually fairly consistent, but sometimes will vary between about 800 RPM and 1200RPM. I have not gotten to checking much more on the car since it has been too cold here in New York to do much. This is my first 914. I have ideas where to start but not certain. I will be having the valves adjusted by a local shop that does a lot of VW's and some Porsches in the next week or two. I do have some fuel leaking at the fuel filler cap, but I do not see enough that I think it would make a difference in the amount of fuel I use.