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!

[Dave_Darling]

The engine needs three things to run: Fuel, Air, and Spark. Of the three, spark is generally the easiest one to lose.

Do you have a good spark? Bring an extra spark plug with you and tape it to a good ground. Hook a plug wire up to it when the car won't start, and crank the starter while you can see the plug. Sparks should be visible in the plug gap. White sparks, yellow or orange is a problem.

Do you have fuel? Do you smell fuel at the tailpipe after cranking for a couple of minutes? When you pump the throttle linkage, do you see the accelerator pump squirting fuel down the carb throats?

Do you have air (compression)? Does the starter motor sound "even" when you're cranking it, or does it have three beats of sound and one of silence? If the latter, suspect a "dead hole" with very low or no compression on one cylinder.

--DD