Dripping Springs

Been plagued for about two months by a problem that I’m taking to be electrical, but who knows? Seems like it started slowly and got progressively worse, rather than suddenly happening.

Here’s the problem: My 12A (rat’s nest deleted) dies while idling when I turn on the headlights or the AC, or even when I apply the brakes and turn on the hazards at the same time. This is an engine from Atkins installed in August of 2020 that has run great until this issue cropped up.

I’m not much of a mechanic, but with direction from smart people (including the previous owner) and a couple of manuals, I’ve taken some steps to try to resolve it, including:

—checked the voltage of the alternator and all looked good
—went ahead and replaced the alternator anyway with one from Rock Auto
—swapped in a different battery temporarily
—buffed up the main battery grounds (on driver’s shock tower and down near the starter), even though they look good
—ran voltage drop tests to those main battery grounds and both looked good
—inspected negative battery cable and it looks good, but maybe I need to replace it
—buffed up a ground on top of the engine
—tried a new ground (jumper cable) from the battery’s negative post to chassis and then to engine
—checked the windows on the carb and I think the floats are at the right level
—replaced the spark plugs, because why not?
—checked voltage and resistance of the coils
—checked resistance of spark plug wires and coil wires

If there was a shop near Austin, TX, that knew how to work on these cars, I’d be there in a heartbeat, but I haven’t found one. I have a great friend who is an amazing mechanic with a full shop, and he has helped with a TON of stuff on this car—and he has offered to look into this when he gets time. But I don’t want to wear out my welcome over there, so I’d like to take any other troubleshooting steps that aren’t outside my capabilities (and many things are). If nothing else, maybe I can compile of list of suggestions I need to try, then my friend can help me do that. He’s a Ford guy, not a rotary guy.

Any thoughts? People keep saying grounds, grounds, grounds, and maybe it is, but I don’t know where to go from here.

Would really appreciate input.

tommyeflight89

iTrader: (4)

So sounds like you have all (or most!) of the electrical bases covered. BTW, what is your measured voltage at the alternator when idling? Should see around 14.4v if I recall.. I had a relatively new Rockauto FB Reman alternator fail on me. The regulator started to go and you could almost see a fluctuating AC voltage on the meter. Had to get the car home by keeping the revs up or it would die.

Hows the idle speed and smoothness? I'm thinking, if you have a vacuum leak, it could bring up a high idle, which you might have dialed out when tweaking the carb. Carb gurus could confirm, but a vacuum leak, with carb adjusted back to 750rpm, could maybe make for a really weak idle. My theory above doesn't sound like it would make sense to just crop up however. As you say the car was running well on the new engine.

Your rebuilt Atkins 12A should make good compression and have good idle vacuum, so maybe there is a leak?!

Dripping Springs

Tommy,
Thanks for the reply.
Honestly, it's been a few weeks since I tested the alternator, so I don't remember exact numbers, but I remember all results being "normal." I could always check again with the new alternator.
Funny you mention a possible vacuum leak. This all started with me noticing RPMs dropping when I stepped on the brake, and we were thinking a brake booster leak. I did my best to rule that out (by disconnecting and plugging the booster hose), and then the problem got worse and began to seem more electrical. To answer your question, the idle is rough and inconsistent. My friend with the shop did adjust the idle because it was high, and then the dying started after that. So that's a great suggestion. Thanks! Maybe I need to hunt harder for a vacuum leak.
Ben

tommyeflight89

iTrader: (4)

Ok yes I would say you need to look at the carb, intake for sure. There are Nikki carb experts here that can for sure help you out.

And good news, most of the work you did on electrical and ignition was good preventative maintenance anyway.

Dripping Springs

Tommy, thanks again. When I think back on the progression of this problem and look at some of the texts I sent to my friend, seems like a vacuum leak is probably the leading possibility. We'll see. Appreciate it.