Battery Voltage Low - most likely culprit?, Does not start well when warm Options

[Chaznaster]

Hi All.

I am having a trouble starting my carbureted 1.8 when the engine is up to temperature (heads at 310 degrees for over 30min). The engine is definitely turns over and the starter engages.

The car starts immediately when cool/ cold. It is also fine when I let it cool after being hot.

My battery seems to have settled out at about 12.2V. Per the Google, that equates to 60% useful charge. That is definitely a problem.

My theory on the non-hot start is that, as copper wire resistance increases with increasing temperature (also something learned on Google), it is just not getting enough current to the coil when hot. Cold wires = lower resistance = better current flow, and so, even with the marginal battery, it gets enough juice to start.

Now on to why the battery is running low. At warmed-up idle speed (800-900 RPM), the multimeter only reads 12.3. That is most certainly the cause of the low voltage.

I'd very much like your input as to whether this is likely caused by a voltage regulator problem or an alternator problem (or both).

EDIT: It will always start with a push start ...

Many thanks!

[Spoke]

At warmed-up idle speed (800-900 RPM), the multimeter only reads 12.3.

@Chaznaster

That indicates your alternator/VR are not working. At idle you should see at least 13V and at elevated RPMs you should see 13.5-14V.

You can easily test the alternator separately. You mentioned the GEN light comes on. That is good and necessary.

Try this:
Ignition off.
Pull the VR or its connector to reveal the connector on the relay board.
Short DF and D+ with a length of wire. This is simulating the VR trying to get maximum voltage from the alternator.
Start engine and measure the battery voltage. It should be around 16V for a good alternator.

If you do get 16V then your VR likely needs replaced.