I may have missed it, but did you make sure the advance diapragm doesn't have ahole in it? It happned to me once and like you, it drove me nuts.
Read what a GM engineer thinks about ported timing. I don't think either manifold or ported would lead to your intermittent problem but manifold vacuum has always worked for me as this engineer recommends. One thing that I would do is to hook up a hand held Mighty Vac tool to it... while looking inside the distributor. Look for frayed wires that can cause a short when the advance plate moves. It may not touch the body every time but if it does it will stumble and fart. Watch it as it moves. Obviously if it won't hold a vacuum, then it needs to be replaced. I once found a very heavy stiff wire used inside a dizzy. It ran fine until you nailed it. When the vacuum dropped, the plate retarded disconnecting the wire from the points and it fell on it's face. When you let up on the gas, the vacuum immediately returned and the plate advanced again reconnecting and restoring the ignition. Take a look inside to see what is happening when the plate is moving back and forth.
Wow, this stuff can drive (or not) you nuts. Had a brand new 355 Chevy crate motor that seemed to run fine. Basicly all I added was a 650 edelbrock carb. Then uder acceleration, or climbing a grade it would ping. Using 91 octane Chevron gas. Finally a shop said to plug the vaccum advance at carb and manifold. It ran like a new engine. I did replace the vacuum tube to carb/manifold. But I intalled a inline smog vacuum reducer that only gives it 3 lb of vacuum I thought that engine could use some vacuum. Actually ran better without any vacuum. Has factory HEI on it.
I know this is pretty old but didn't want to start a new thread on same problem but I'm also having advance problems in our '47. It a Ford FE 390. Vacuum advance is new as of yesterday and new vacuum line. It advances fine with it disconnected but when you connect it and rev the motor it looses #1 cylinder at around 20 degrees. With the timing light connected it quits sending a signal at this point. Seems like it would be something going haywire inside the distributor. Any thoughts?
Are you checking advance with the light with it hooked up? I sold that crane points eliminator and switched to a dual point mech advance only dizzy....no problems
Only to see where it starts breaking up. Set it and initially checked it with vacuum advance disconnected. I am thinking about going to mechanical only dist. also.
Not all engine combinations benefit from vacuum advance Crane sells the adjustable one to limit how much you can use, at some point you lose whatever benefit you gain from it...in my case the engine runs no hotter, or different and I had it hooked to both manifold and ported vacuum.
Got it figured out finally. Crazy thing is the points were set too wide and the vacuum advance really exaggerated it when hooked up. It was also breaking up a bit without the advance hooked up but at a higher rpm. Drove it to church tonight and it runs a hundred times better. Hopefully mpg will increase some due to this correction. Was only getting 9 mpg. If it'll get 12 mpg I'll be tickled.
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