To test for spark, make sure the body of the spark plug is grounded to the engine.

You don't want the energy of the CDI (or an IDI) discharged through the coil, without a path for the spark to go to ground. You can damage the coil or the CDI that way. A lot of people have done that inadvertently and not caused their ignition to fail, but it ain't good practice.

Too Many Speculations………..
 

You have too many speculations in your analysis. Instead, test and confirm those ideas. Hook up a pressure gauge and an inductive light. Confirm the cold control pressure and ignition signal @ START. Borrow a good working ignition coil from someone. Your CIS is not igniting fuel. Apply some starting fluid for the test. This problem will not go away.

Tony

That plug is not working. I went to the Bosch website and found no listing for '73, but for '74 they recommend 7992 copper nickel. Original plugs were Bosch W 235 P 21. Pelican only has listings for NGK so it seems Bosch no longer has plugs for '73. That could be your issue if the spark plugs are wrong.
Personally I've always been a fan of NGK. NGK website recommends BR7ES.
As far as your observation about the change in pitch of the fuel pump, it is interesting. There should be a few seconds for the fuel pressure to build. It is probably nothing and may well be it is working properly considering your pressure test results.

FWIW I have been using BPR7ES (BP7ES until they became unavailable) with great success.

Pretty much any plug will start the engine. They may not work well at full power and high temps, but when the engine is cold, the spark plugs are cold, so it doens't matter for starting.

I don't know if I can agree or not with that Pete. From my perspective the spark plugs in post #77 look like they are not running hot enough to burn clean and are leaving a lot of deposits. In this case it seems to still start, but if the ignition system is not totally compatible with the spark plug, some may produce a spark but not strong enough to get enough combustion to start.
My searches of NGK and Champion also only recommend copper core plugs by the way. None show platinum or Iridium. I thought I'd get a screen shot of my Bosch website search, which returned no results for '72-73 2.4l 911T.
http://forums.pelicanparts.com/uploa...1715008175.jpg

Just to touch on the micro switch topic. I have noticed used prices starting around $70+ for these, since the original Kissling are nla. A new superceded switch 911 613 106 01 start around $150+, which look a lot like Honeyweel below. Picture of my '73.5 on left as well as previous mfi that came with some assorted parts I bought.
http://forums.pelicanparts.com/uploa...1715008837.jpg
I decided to search around a bit. It seems the dimensions on these are pretty standard. Honeywell seems to have a few alternatives in the $30 range. The main difference is in arm length and style, which could be cut to fit. Then you can save the original for concourse time.
https://sps.honeywell.com/us/en/products/advanced-sensing-technologies/industrial-sensing/industrial-switches/basic-switches/large-basic-switches
http://forums.pelicanparts.com/uploa...1715008699.jpg

I would like to read the CO from my car. I do not want to cut/weld in a bung. I tried a local smog guy to see if he had an old CO sniffer that slid into the exhaust. He did not.

I see lots of CO readers available online. Some are expensive, some are cheap. I don't know which ones have exhaust sniffers that would actually work.

Does anyone have a suggestion for type of device I would want to get? I posted a separate request on Pelican to see even if anyone had one local to borrow. But I did not get any responses.

Jay, you will want the AFR gauge in your car eventually. Just bite the bullet and install one now. Yes, you will have to use a holesaw to cut hole in the exhaust pipe, then weld in a bung. I you don't have the equipment to do this, find a shop that does. .

I had a bung installed in my SSI's when I was running an '86 3.2 in my car. Fortunately I had someone I trusted to weld stainless.
Wayne commented in a thread on the engine forum yesterday "I have an LM1 (and LM2) which I use. Not the greatest tool in my opinion, but it gets the job done (most of the time)".

I've been quiet because I haven't had time to work on it - and I tried swapping to another WUR since that is the only thing I've changed recently to see if that was it. Nope. Still happens. The one thing I'm seeing as more consistent is that it won't even try to start on the first tries with the throttle up. But once I put the throttle down, it gives a little kick until it starts. I wonder if the CSV is putting TOO MUCH gas in and flooding it. Could that be possible? Is there as way to test?

The only tests for the cold start valve is to run the fuel pump for 1 minute and check for drips or leaks, and with 12v supplied that it has a good conical spray pattern.
No quantity of fuel is given.
I'm wondering if your initial setting is a bit rich, although it could be a leaking injector or cold start valve. Looking at you spark plug pic, I would think your in the cold to rich, with perhaps a dash of oil category. Do all the plugs look the same?
http://forums.pelicanparts.com/uploa...1716214650.jpg

For the heck of it, to help zero in on the right fuel mixture adjustment, I bought an AFR gauge and hooked it up to the 911 with the adapter that goes into the exhaust pipe. I'm getting odd results and I thought I'd see if anyone had thoughts.

The book says my 73.5 should be at 2.5-3% CO% at idle. The AFR conversion for that is 13.38-13.56.

When I set my car at that, the car idles nicely at 900 rpm, but when driving it, it is noticeably less than smooth. Not remotely acceptable. It runs at 14.5 AFR at constant throttle at about 45 mph - and like I said, not smooth, kind of fluttering.

If I richen it by about 1/2 turn, I get to about 10.3 AFR at idle, 12.5-13.5 AFR at that same 45 mph, and it's nice and smooth. But, the idle hunts a bit unless I lean it out to just over 1,000 rpm. This has been where I have been running it before having the AFR gauge.

FWIW, on the starting situation, when it is at the richer adjustment, to start the engine I first start the starter without the throttle, nothing happens, stop starter, re-start starter with throttle, and it ultimately starts on the second attempt after spinning a bit.
When it is in the leaner adjustment, it gets some ignition, but won't fully start. And I have to do it multiple times before it will start. It takes longer on the leaner adjustment than the richer adjustment until it actually starts. But it gets some ignition earlier.

Does this suggest I have an air leak in the box that I didn't find when I did the smoke test?
Does it suggest anything else to anyone?
I may will explore the cold start valve again.

As a reminder, the car starts Ok when fully cold. Starts great right after turning off the car. Starts great for about 4-5 minutes after turning off the car. But starting at about 5 min it is harder to start the car and stays hard for a couple/few hours.

Yeah, I know what you mean by the "flutter." Really hard to chase down too, because minor air leaks or ignition misses can feel the same.

This thread is getting long and old, so let's recover some ground. Did you do a compression test and was it good? Valves adjusted correctly, or even a little loose? Injectors tested on the engine and you have even fuel delivery to all cylinders? Timing is correct and the dizzy is advancing properly?

It sounds like you still have an air leak somewhere that is leaning one or two cylinders at high vacuum. If the engine runs smoothly under high load, that is a strong indicator that your ignition is working correctly, and that you have an air leak, because under high load, the engine has low vacuum, so less air gets sucked into the intake; AND it is injecting much more fuel, so the dilution of AFR due to leaking air is much less. Also, enriching the mixture screw to get it to run smoothly further indicates an air leak, and further contraindicates an ignition problem.

But I have to admit, chasing air leaks on those old CIS systems is frustrating. And the ignition could be adding to the issues. BTDT.

I was just speaking with Bob Ashlock, who rebuilds CDI units. He said that there is a failure situation where heat causes issues with the CDI (where heat from sitting impacts the CDI, but once the car is driving, the air flow keeps the CDI cool enough). Since I've run through the gamut of everything else, I'm going to send him the CDI unit for testing and possible repair.

Fingers crossed!

And in the meantime, I will look again for leaks.

If it misfires under part load, but not under full load, then it's not the CDI box. If you were having a CDI problem, it would misfire the same or worse under full load.

Bob reports back that he tested the CDI and it is completely to spec, and he even puts it in a hot box to see if he can trigger it to fail from heat. Nope. Working just fine.

;)

Back to looking for air leaks.

Well, Tony offered, as he is known to do, to have me send him the CSV for testing. It seems he may have helped fix it, but I may not even have to send it to him. I pulled off the CSV and on closer examination of the o-ring gasket, I do not have a high level of confidence in it. I suspect I have been leaking there. That could explain the hard start problem and CO level. I will be getting a new o-ring and checking. Fingers crossed.

Here is an update, and new question. I did a smoke test again and found my pop off valve was leaking. It pulled off and I found it has now been glued on twice! The valve also did not seal all then way when at rest. I bought a new one, this time I Dremeled down the fins and glued it right down flat - and I used a 3M glue for nylon based materials. And lubricated the o-ring - I can't say I ever knew to do that. Anyway, that solved that leak.

But it really didn't address anything. Car still runs great, except light throttle and starting is good, not great. I could just live with it, but I want to get this better.

I blocked off the decal valve in case it was leaking. Didn't seem to change anything.

I did another smoke test. This time I found trace smoke coming out of the throttle shaft (at least I think that is where it is coming from). I think that could be a source of my problems. So, I've searched this site and found this: https://forums.pelicanparts.com/porsche-911-technical-forum/1158420-cis-throttle-body-re-bush.html

I also sprayed some starter fluid on the throttle shaft while it was at idle. It caused the idle to drop.

I will continue on that post to see if there is more info to be had.