1981 AC: Cutting out at startup without applying gas

[Wildthings]

The "P" shape is normal. The shape has to do with the closing rate, the AAR initially cuts the air off fairly quickly and then slowly cuts it off the rest of the way.

[Wasted youth]

No need to test the AAR with a heat gun. Put 11-12 volts to it and give it about a minute to a minute and a half. If it’s working, you will see it change. It has a strip of metal that is indexed to the aperture inside and the strip deflects when the wire wrapping around it heats up. The deflection operates the aperture.

I learned all this last month testing three of mine. I took two of them apart and took pics. Hope to post them today, but I’m focusing on getting my ‘81 through the smog check then finish registration so my son and I can camp this week.

[Scottn59c]

10 minutes in the oven at 200 degrees did lead to the AAR closing up almost all the way (see picture). So it can open and close. I guess the question is whether or not it is opening and closing as efficiently as it should to get the proper air mixture going at startup.

I'm not sure whether I can conclude that this AAR is okay and move on to the next possible culprit. I feel kind of like a dufus for continuing to post these questions, but I'm sure someone else will have them later down the road, and if this helps him or her, that's a good thing.

Should I be concluding that the AAR is not my problem?

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Farfignewton!

[jberger]

I’d say it’s safe to assume that’s not your problem.

This system is quite fragile... in order for it to start, warm up and operate smoothly everything needs to be tip top.

Have you checked valve adjustment and leak down?

J

[Wasted youth]

Allow me to say this... using ambient heat could give you a false conclusion. Reason is the metallic strip heats up by the wire wrapping.

So if you heat it up in the toaster, yes you can get the sucker to do its job. But you cannot verify if electrical current will do what it is supposed to, right?!

So... how would you know if it works as intended? By applying 11-12 volts and watching it.

[Scottn59c]

Guys,

You are awesome - thank you all so much for the thoughtful advice thus far.

I went to reinstall the AAR and discovered this rubber pipe that had become disconnected from the engine. It looks like it had been JB welded on there? Not sure if it came unattached when I was monkeying around with the AAR or not, but whether it did or not, it definitely wasn't on securely.

How should this thing be sealed? Do you think it's part of my problem with the idling issues?

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Farfignewton!

[jberger]

Most likely not... that’s part of the evap charcoal canister piping.

J

[Buggeee]

[Wildthings]

In the long run you will want to have the nipple brazed in place. But for now anything that will hold it in the tin will work. As others said it is not going to be your problem.

[Wildthings]

[kublerwagen]

And then vacuum leaks, checking for them. Once you are done checking them, then it is time to check for vacuum leaks. Only sort of kidding. I had checked and checked and a friend brought his LM-1 “smog sniffer” over and we spray checked again. Found more.

I suggest going to the Itinerant Air-Cooled Forum and finding (or asking) for Colin’s troubleshooting guide. The comment above about the system being fragile is accurate. You’re on the right path but it is going to be a process of checking and rechecking everything as you go. The bonus is that you’ll find a myriad of less-than-ideal things along the way you can fix and become much more comfortable and confident in your engine.

[Scottn59c]

I wanted to post an update on this thread for anyone else who runs into the same problem (and I have seen a few such posts over the last year or two).

What solved the issue for me turned out to be an engine head temperature sensor spacer. I found one for a Porsche on eBay, and it's a cylindrical spacer that screws into the engine on one end and the sensor on the other. The spacer prevents the aging L-jet system from getting too hot during the warmup cycle.

The part cost me about $20 (you might find or even make one cheaper), and the engine now holds strong off of a cold start.
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Farfignewton!