Volkswagen: Rotates but will not fire, electric fuel pump, vacuum leaks

Question
I have a dual port type 1 engine Problem: Engine Cranks & Rotates but will not start.
It use to run, but had this ominous "pop" or back fire every once in a while, then it stop running altogether.
I installed a new Pertonix ignition system and added dual carburators. The distributor does send spark to all 4 plugs, (yellow not blue) but still doesn't fire up, not even hint of combustion, assuming a lac of gas, I added and electric fuel pump.....same problem...could this be a carb Problem? coil problem?, bent valves or what?...


Answer
Mike,
 There are many details to check, but generally it's either:
- Low/no fuel delivery(bad fuel pump, clogged lines/filter, bad tank pickup, rust in tank and/or lines)
- Bad/contaminated fuel(water?)
- Carb fouling/varnish (old gelled fuel/dirt in jets and other parts)
- Carb malfunction(stuck float, worn leaky throttle pivot)
- Intake air restriction(clogged filter, mis-adjusted throttle linkage, rat nest?)
- Vacuum leaks(carb gaskets, intake manifold gaskets)
- Spark timing is off(distributor mis-adjusted, wobbly/bent distributor shaft, cheap cap/rotor, main pulley not properly installed, timing marks incorrect, timing set for wrong engine series)
- Weak spark (bad wires/coil/condenser, wire crossfire(cheap wires))
- Low/no cylinder compression(worn rings, valve guides, valves bent, heads not securely bolted, cam timing is off, broken internal engine components)
- Excessive back pressure (bad/clogged/improper muffler)

Check out this article:
http://www.vw-resource.com/car_wont_start.html

- Rick