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]

Thanks everyone - this is all really helpful and good to know I was more or less on the right path.

To your comments:
@Fixer34 : The alternator light does come on. It also sometimes flickers at idle.
@emerygt350 : I do not recall having the issue in past years, but we are driving the car more often and longer distances so may be overall heating up more? Also, do you have a link to the adjustable voltage regulator? That sounds interesting.
@914Sixer : I do have all the wiring in place having pulled the engine and gone through it all a few years ago. The battery is getting a charge, just not enough it seems.
@brant : It is a carb car. The infamous center mount Weber 32/36 so not so close to the heads. (There is a set of 40 IDFs on my bench waiting for a rebuild - maybe next year!) I also have spacers ...
@930cabman : I think I will have the started checked out, but only after driving season is over!

I'll come back to this once I get it figured out. It may be a few months.

[emerygt350]

Thanks everyone - this is all really helpful and good to know I was more or less on the right path.

To your comments:
@Fixer34 : The alternator light does come on. It also sometimes flickers at idle.
@emerygt350 : I do not recall having the issue in past years, but we are driving the car more often and longer distances so may be overall heating up more? Also, do you have a link to the adjustable voltage regulator? That sounds interesting.
@914Sixer : I do have all the wiring in place having pulled the engine and gone through it all a few years ago. The battery is getting a charge, just not enough it seems.
@brant : It is a carb car. The infamous center mount Weber 32/36 so not so close to the heads. (There is a set of 40 IDFs on my bench waiting for a rebuild - maybe next year!) I also have spacers ...
@930cabman : I think I will have the started checked out, but only after driving season is over!

I'll come back to this once I get it figured out. It may be a few months.

This is the regulator. The weird Amazon knockoff brand I bought isn't available but here is a different weird Amazon knockoff brand
https://a.co/d/0kzku6V.

I would suspect it is just carbs being carbs. I assume you have tried the old hold the throttle open as you turn the key? Do not pump it of course. Nobody has good things to say about that central carb but it definitely won't cook like the others. You are probably just getting too rich of a mix for a hot engine.