924 Sometimes wont start

[gronquist43]

I have an 1987 Porsche 924. Sometimes it just will not start other times it will start and run just perfect as if there were never any problems at all. I am sure it is an ignition / spark issue as when it does not start if you pump the gas some you can smell it so I know it is getting fuel. I put a new cap and rotor on it and no difference, the car has been sitting for a few years but i allways start it every few months or so.
Does anyone have any ideas where to even start looking first?
Thanks,
Guy