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!

[Chaznaster]

Tons of great ideas here - thank you all. I'll start working through the different tacks.

In the meantime, by checking the alternator harness, is it simply continuity through each wire, or should I be checking resistance, as well?

[Spoke]

In the meantime, by checking the alternator harness, is it simply continuity through each wire, or should I be checking resistance, as well?

I think you're going too deep too fast. Generally wires and connectors do not cause these types of no-charge issues. Try doing the test I outlined previously. You will at least be able to measure the output of the alternator.

Another test is to run the engine and measure the voltage at each of the 3 wires to the alternator (D+, DF, D-) and battery voltage to chassis ground.

D+ should be 14V
Battery should be 14V
DF should be 5-9V
D- should be zero

Measure at the VR or alternator connector. You can learn a lot about the charging system with this simple test.