Beetle totally refuses to fire. Any ideas?

[MountainBeetle]

The weather reached minus 5 Celsius (below freezing), and I hadn’t reduced my spark plug distance in anticipation of really cold weather. In this sudden cold the revs would drop randomly every minute or so, and when accelerating the Beetle would bog down. It would be pedal-floored but only after a few seconds there was a slow acceleration, like driving through treacle. I was able to quickly tune it so the revs would be higher, then when gunning it along the motorway it was like it had no issues.
Next day I tried to properly tune it and this is where the bigger problems began. Initially it would struggle to maintain an idle, then would backfire a bit, and then like the day prior, it would begin bogging down and I’d have to pull the accelerate lever at the engine to keep it from stalling but again it would take a few seconds to begin to rev up.
Fuel was getting into the engine ok as I can smell it.
Next the sparks became irregular until after maybe the 20th time fiddling with the tuning screws on the carb, it just wasn’t sparking, just the occasional half-hearted spark and now 2 days of efforts have failed to start the engine.
It’s not a starter motor issue as it is trying well. It’s not the battery or voltage as even when attached to a starter pack it can’t get sparked to turn over, just the very occasional splutter that never leads to anything.
I’ve resized the spark plugs to cold now back to regular as the weather is mild again. I’ve replaced the spark plugs, changed in and out a new bunch of spark plug cables, I’ve changed in and out two coils, and checked all the wires. I’ve also changed the distributor cap, rotor head and points (correctly distanced) and no spark or improvement. I’ve sprayed in starter fluid too into the air intake, but to no effect. Any ideas, folks??
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1969 Beetle, 1978 Beetle, 1978 T2 Panel Van

[busdaddy]

Around here "turn over" means the starter is rotating the engine, it sounds like what you are lacking is "firing".

All of this altering spark gaps and stuff for cold weather is news to me, it should run the same at +40 as -40, you might have multiple issues and your fiddling may be contributing to them.

The first thing I would do is connect a test light between the primary terminals on the coil, does it light up when you turn on the key?, does it blink on and off when you crank (turn it over)? You may have ignition switch problems.
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[MountainBeetle]

[MountainBeetle]

Although this may be one issue, do you have any idea what caused the sudden bogging down? It just seemed so odd and occurred without warning.
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1969 Beetle, 1978 Beetle, 1978 T2 Panel Van

[busdaddy]

Sudden problems when cold?, water in the fuel, non functioning manifold preheat and non functioning aircleaner preheat are all prime suspects. Add in some aftermarket Chinese ignition or fuel system parts and things can get really strange.
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[MountainBeetle]

This was pretty much what I was like:

Link

Seems an air leak check could be something to add to my to-do list.
https://itstillruns.com/symptoms-carburetor-air-leak-6902940.html

Link

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1969 Beetle, 1978 Beetle, 1978 T2 Panel Van

[Cusser]

[ashman40]

[heimlich]

Check to make sure you are getting 12V at the coil when the ignition is turned on.
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[MountainBeetle]

[MountainBeetle]

[heimlich]

[Cusser]

[bsairhead]

[Eric&Barb]

Please do edit the title replacing "turn" with "fire" for future searches to help others.
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In Stereo, Where Available!

[MountainBeetle]

[MountainBeetle]

This is an example of it not firing

Link


A multimeter check finds the battery is fine, the new coil is fine (3.6 primary winding, 7.44 secondary winding).
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1969 Beetle, 1978 Beetle, 1978 T2 Panel Van

[busdaddy]

I wanna see a vid of you cranking while a test light is connected between the primary coil terminals.
_________________
Rust NEVER sleeps and stock never goes out of style.

Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!

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[MountainBeetle]

[MountainBeetle]

Regarding flooding being an issue to troubleshoot, do you know what the “white cable” on “coil connector one” means as I have no white cables, as seen on page 59 of the Beetle manual:

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1969 Beetle, 1978 Beetle, 1978 T2 Panel Van