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!

Alternator and/or voltage regulator are likely suspects since voltage at the battery should be in the 13.5v range while running.
BUT, does the alternator light in the combo gauge come on when you first turn on the key? If it does not, check/replace the bulb, then check the wiring. Silly as it sounds, the bulb must light up before starting/running the car for the alternator to work.

I am a fan of the adjustable digital voltage regulator. However, not sure that low voltage (which you do want to fix) is it. Many carbed cars struggle with hot starts. Even old fi cars struggle. Is this a new thing or has it always been tough to start when hot?

Often missed item is the alternator wiring harness.

You have adequate voltage to turn the starter
You can check the voltage warm at the coil, but the coil draws much much less power than the starter. So if the starter is working…generally so is the coil

I propose that it’s a carb car

Do you have phenolic spacers on the intakes
Is it possible you’re struggling to start because it’s flooded?
Often the hot motor when turned off.
Will boil the fuel from the carb bowls. That runs down the intake and floods the spark plugs

Just sayin, I have a family member who is raising their child on advice from said information source. More than a little scary

back to the original issue, I would pull the starter and send it to the shop for inspection. Windings might be getting weak

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.

You’ve got multiple problems going on. 1st not charging properly.

Check the voltage at the coil - when it is hot, and while you are cranking . I suspect you are going to find the voltage is very low while cranking. I’d bet that it’s probably 9v or less and you are getting a terribly weak spark; not enough to light off; especially if mixture is already a bit rich when hot.

When you push start, the starter motor load doesn’t drag down the voltage at the coil and you get a decent spark, enough to start it.

Measure coil voltage while cranking as was suggested by Brant. Fix charging problem. See where you’re at. There are plenty of other diagnostics that can be done. No need for guessing.

Use a decent battery charger to bring the battery up to full charge. Report back what the battery voltage settles to after a few hours off of the charger. Proper voltage is about 12.8V. As Peter says, when cranking off of the battery the voltage will drop drastically, and a weak battery will drop even further. If you have a battery at 60% it will soon leave you stranded.
As Mark says, check the alternator harness. I checked out 10 or 12 harnesses not long ago and every one was bad!
Read this thread also: http://www.914world.com/bbs2/index.php?showtopic=371628

@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.

Click to view attachment

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?

0 resistance

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.

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

I am back with some data ...

Battery after full charge and 3hr sitting : 12.5v

Battery with VR removed and DF / D+ jumped : 17v (at 1200 RPM. Did not get this at 850 but expect it would be low)

Alternator to ground
At 1200 RPM
D+ 13.6v
D0 0v
DF 5v

At 850 RPM - note alternator dashboard light often flickers here
D+ 0.7v
D0 0v
DF 0.5v

I recently cleaned the ground between the transmission and body, as well a the multi chassis ground below the relay board.

Do alternators or VRs start by failing at the low end of voltage range?

Thoughts??

Giving it some thought, I would probably conclude that the VR is the issue.

@Spoke what do you make of the numbers.

Thanks.

Replacing the VR is so easy and cheap, it might as well be your first move. Buy the stupid cheap adjustable version I posted above. If it doesn't fix your problem you will still have a better VR than the old analog points version you have now.

I’m trying not to be an engineer my can’t help myself

All these voltage regulators are analog. Yours is solid state but still analog.

Solid state doesn’t equal digital.

Yea im crazy I’m an analog man in a digital world.


https://www.youtube.com/watch?v=6YkAnv8inQE?si=Af0KIz_58Xzr23Ip

OK that number looks good for the alternator at maximum output. Was this the battery voltage?



If you measure these voltages again, please measure the battery voltage as well.

At 1200 the numbers look good. D0 being zero is expected. Also D+ and DF looks good.

At 850, did you measure these voltages after doing the 1200 test? Or a different run? With D+ at 0.7V, the alternator is not functioning.

If you go from 850 to 1200 then to 850, does DF go from 0.7 to 13.6 then back to 0.7?

I got back to the car today and retook measurements after ensuring it was completely warmed up.

850-900 RPM
D+ = 0.80
D- = 0
DF = 0.61
Batt = 12.2

1000 RPM
D+ = 12.3
D- = 0
DF = 6.5
Batt = 12.4

1400 RPM
D+ = 13.7
D- = 0
DF = 5.0
Batt = 13.3

2000 RPM
D+ = 13.3
D- = 0
DF = 3.3
Batt = 13.2

If I go to 1400 then back down to 850, The numbers come back down.

So no alternator output at low levels ... does that point to a rebuild?

Many thanks.

Starts fine when cold? When it’s hot it still spins up, just won’t catch? Have you considered hot fuel? When you are starting when hot, are you touching the gas pedal? My car (Webers) stumbles at startup when hot. 3 pedal pumps then feathering the pedal. You have to get those throttle plates open. Things calm down when the carbs are full of fresh tank fuel. Actually it’s only a few seconds. Are you using phenolic spacers/gaskets on the intake bases? I thought the voltage numbers were more about what the ‘brain’ needed to function.

You want 13.5 at idle. After I switched to a modern VR I get 13.7 at idle and 13.7 at whatever rpm you like. At the battery. When you have to turn your wipers on and your heater blower and your cool air blower and your headlights you don't want to be wondering about your battery.

@Chaznaster
When you go from 1400 to 850, does D+ go back to 0.6V? D+ at 0.6V means the alternator is not running.

One other test to do is the D+ to DF short with VR pulled. Check D+ and VBATT at 850, 1400, 2k. Do them quick since D+ shorted to DF is maximum output. I would want to know if the alternator can work at 850.

It starts great cold and most of the time hot. I have a single, central Weber 32/36. It is not over the heads so should not get excessively hot. I am running the spacers, as well, just in case. I usually give it a single pump on the throttle to reset to fast idle. When it does start it comes right to life.

When I go from 1400 to 850 D+ does go back to 0.6V. And back up upon returning to 1400.

I'll try the next test and get back as soon as I have some more numbers.

As always - thanks.

EDIT: This might not make any sense, but could the belt be slipping at low engine speeds. I would think that would happen when fast ...

Just dealt with this on my green car. Replaced the VR and battery and running 13.5-13.7 all the time now.

That is weird that going from 1400 to 850 causes the alternator to turn off. Usually once the alternator is bootstrapped it keeps on running.

BTW, when at 850 and V+ = 0.6V, is the GEN light on?


About the belt, it should be tight. Is it?

That would be better than an alternator rebuild ...

And congrats on the Bumblebee project!

At 850 the gen light is flickering. It goes out as soon as I rev the engine.

I'll check the loose belt and do other tests this weekend. I recently had the engine out and pulled the alternator / replaced and tensioned the belt but maybe I did not get it right ...

So ... I feel a bit foolish about this ... the cause of the wonky alternator voltages was a loose fan belt. Must have been slipping at lower engine speeds.

Thanks to all for all the help, as always. Special thanks to @Spoke for walking me through the diagnostics.

Now we will see whether we still have a hard start when warm.

Don't feel bad, happened to me after I rebuilt my engine. I freaked out for a couple days and then realized I was hearing some strange sounds...