1. Verify Ignition System Basics:
* Spark Plugs: Are they new and gapped correctly (usually around .035"-.045", check your specific plug's recommendation)? Remove a plug, reconnect the wire, ground the plug to the engine block (metal part, not the paint), and crank the engine. You should see a strong, consistent spark. If not, move on to the next steps. If you DO get a good spark, the problem is elsewhere (likely fuel delivery despite you saying you have gas at the carb).
* Spark Plug Wires: Are they properly seated on both the plugs and the distributor cap? Inspect the wires for cracks or damage. A cracked wire can cause a misfire or no spark at all.
* Distributor Cap and Rotor: Inspect these for cracks, corrosion, or carbon tracking. A worn or damaged rotor can prevent spark from reaching the plug wires. If they look suspect, replace them.
* Distributor Timing: Double-check your timing. Even if you think it's correct, it's easy to be off slightly. A significantly advanced or retarded timing can prevent firing. Use a timing light to verify the timing mark aligns with the specified degree on your harmonic balancer at idle.
* Ignition Coil: Check the coil for cracks or any visible damage. A faulty coil won't produce the high voltage needed for spark. You can use a multimeter to check the coil's resistance (consult your workshop manual for specific values).
* Ignition Switch: Make sure your ignition switch is working properly and providing power to the ignition system.
2. More Advanced Troubleshooting (if the above is okay):
* Pick-up Coil (in the distributor): This is a common culprit. A faulty pick-up coil won't send the signal to the ignition module (or the points, if you have points ignition). This requires testing with a multimeter or a coil tester.
* Ignition Module (if applicable): If your system uses an electronic ignition module (most likely on a 305), it could be faulty. These are harder to test without specialized equipment. A swap with a known good module is the easiest test.
* Wiring: Trace all the ignition wiring from the coil, distributor, and ignition switch. Look for loose connections, broken wires, or shorts.
* Crankshaft Position Sensor (CKP) (if applicable): Some electronic ignition systems use a CKP to tell the ignition module the crankshaft's position. A faulty sensor will prevent sparking.
3. Fuel Delivery (double-check, despite you saying gas is at the carb):
* Fuel Pump: Although you say you have fuel at the carb, a weak fuel pump might not supply enough pressure for proper atomization. Check the fuel pressure.
* Fuel Filter: A clogged fuel filter can restrict fuel flow.
Important Considerations:
* Workshop Manual: A Chevy 305 workshop manual is invaluable for this. It provides specifications, wiring diagrams, and troubleshooting guides specific to your engine.
* Multimeter: A multimeter is essential for testing various components in the ignition system.
In short: Start with the simple checks (plugs, wires, cap, rotor) and systematically work your way through the ignition system. If you're uncomfortable working with electricity, seek the help of a qualified mechanic. Don't proceed if you are not familiar with automotive electrical systems as you could damage components or injure yourself.
