* Heat Soak and Ignition Advance: The most likely culprit is that your ignition timing is advancing too far when the engine is hot. The increased heat can affect the components in your ignition system (distributor, coil, etc.), causing the timing to advance beyond the optimal range. This excessive advance can lead to detonation (pre-ignition) when the engine is warm, causing the engine to resist cranking.
* Distributor Issues:
* Vacuum Advance: Check the vacuum advance mechanism on your distributor. A malfunctioning vacuum advance can cause erratic timing changes as the engine warms and manifold vacuum changes. Test the diaphragm for leaks.
* Mechanical Advance: The centrifugal advance weights in the distributor might be sticking or wearing out, causing uneven or excessive advance as the engine RPM increases.
* Distributor Cap and Rotor: Although you say everything is new, ensure the distributor cap and rotor are correctly seated and not cracked or damaged. A faulty cap or rotor can lead to misfiring, making cranking harder.
* Other Possibilities (less likely given "everything is new"):
* Fuel Delivery: While less likely given your description, a fuel pump that weakens when hot could contribute.
* Compression: Low compression in one or more cylinders would make starting harder, but this would likely be present both hot and cold. A compression test would quickly eliminate this.
* Starter Motor: While you said everything is new, a faulty starter solenoid or a weak starter motor could potentially contribute to slow cranking, especially when the engine is hot (increased resistance).
Troubleshooting Steps:
1. Check the timing: Start with a baseline timing check when the engine is cold. Then, let the engine run until fully warmed up and re-check the timing. Compare the readings. A significant advance at hot temperature points towards the issue. Make sure you're using a timing light, not just the mechanical advance on the distributor.
2. Inspect the distributor: Carefully examine the vacuum advance diaphragm for leaks and the mechanical advance weights for free movement.
3. Test the ignition system: Check the coil, spark plugs, wires, and distributor cap and rotor for proper function. A weak spark when warm exacerbates cranking difficulties.
4. Check fuel pressure: Monitor fuel pressure cold and hot. If it drops significantly when hot, suspect the fuel pump.
5. Compression test: While less likely, a compression test will give you vital information about the engine's health.
If you're not experienced with auto repair, it's best to take it to a qualified mechanic. Improper timing adjustments can cause serious engine damage. Describing the problem clearly as "lag when cranking *when warm*, even with all new parts" will assist the mechanic greatly.
