GM-GMC: distributor?, fuel pressure regulator, chevy g20

Question
Hi. I have a 1986 chevy G20 305 van (gasalione)
I have had problems with it not starting it turns over but don't start, I have had a tune up done, put in a new igniyion switch, new fuel filter, tested the started and alt. and they tested fine. Retested the module and seeing it is also new it was okay. Replaced the battrey, and it srill won't start, any ideas on what it could be?
Any help would be greatly appreciated as this is really starting to get a little costly to figure this out and then it still won't start. I should mention that after replacing switch, it started but after it sits for a day or 2 than it won't,
when I change the little condensor(silver tube looking thing in the distributor it started, but once again not after it sat for a couple of days. Had the coil tested it was ok too.

Thanks

Answer
I would look more at the fuel system since changing all the parts and checking the ignition system did not cure the problem.

Your description sounds like a fuel pressure regulator that allows the fuel system to lose its prime, or an intermittent electrical problem at a connector in the fuel system.

A gas engine needs three things to run:  Air and fuel mixed in the correct ratio, properly timed spark, and compression.