Engine runs poorly spontaneously?

[Rusty Nail]

matter of fact - there is a test for that...u can measure the resistance and perform a "sweep" while you make sure it moves smoothly with no gaps.
or something.

 

[motionz]

By now, everything from the battery to the ignition has been measured and/or replaced:

- +12V cable from starter motor to fuse box
- from fuse box to starter switch
- from starter switch to neutral switch and distribution cap
- from neutral switch to starter motor solenoid
- new distribution cap + rotor + HEI module + ignition coil + spark plugs + spark plug wires
Unfortunately, this had no effect..

While measuring the ignition timing, I manually pull the throttle on the carburetor and felt around for leaks with my fingers. Exactly behind the heatpipe choke unit, I felt a strong suction effect. The suction spot was not visible! but I removed the Impco set and carburetor, and this is what came to light! see pics
I had a spare gasket but it's a different model see pic. can I use this gasket? a small section between the throttle valves is then not covered

@75gmck25 the intake manifold is original cast iron

 

[75gmck25]

You definitely found the source of a big vacuum leak!

There are multiple gasket configurations for a Quadrajet, and I find it’s difficult to know for sure exactly what coverage of the base is critical. For now you might just try the other gasket and see if it runs better.

The typical solution is to look up the carb number for the recommended gasket. It might take a while for shipping from the US, but at least the part is really light.

 

[Rusty Nail]

dude.
you're going to have so mush POWA!

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[NLD79K10]

@motionz I think that gasket under your Q-jet is the FelPro 1908. Pretty sure I saw that AJ Speedshop in the Netherlands had that gasket in their webshop when I last looked around for one.

 

[motionz]

Yes, finally a major find that is most likely the cause!
Although I still find the irregular spark plug spark suspicious.

But first, replace the base gasket; it is a Quadrajet Rochester model number: 17058508.
I think it is the M4MC carburetor type with a hot air choke.
I ordered a gasket set from my new supplier in the Netherlands (Rockauto no longer supplies to the Netherlands), see pic.

 

[NLD79K10]

Yes, finally a major find that is most likely the cause!
Although I still find the irregular spark plug spark suspicious.

But first, replace the base gasket; it is a Quadrajet Rochester model number: 17058508.
I think it is the M4MC carburetor type with a hot air choke.
I ordered a gasket set from my new supplier in the Netherlands (Rockauto no longer supplies to the Netherlands), see pic.

Just ordered a bunch of stuff from Rockauto myself with no problems getting them supplied to the Netherlands. It's just that with the economic sanctions on Russia due to their invasion of Ukraine, imports of parts from manufacturers that do not provide certification that they were not manufactured using Russian steel into the EU and UK are banned. This can limit your choice of brands for certain items. For example for my K10 I can't order Bosch or Dynamic Friction brake pads from Rockauto but I can order Raybestos ones. It's a bit annoying at times but you can still get stuff shipped in, provided the manufacturer has submitted their paperwork.

 

[motionz]

strange i get the message when i checked out that a "new European packaging law is active (PPWR)" ? Maybe it has changed in the meantime you never know..

 

[Rusty Nail]

matter of fact - there is a test for that...u can measure the resistance and perform a "sweep" while you make sure it moves smoothly with no gaps.
or something.

You must be registered for see images attach

xc_hide_links_from_guests_guests_error_hide_media

You must be registered for see images attach

you are likely building on a bad foundation.
I want to "double down" on the pick-up coil.

 

[motionz]

The piece who was sucked out of the carburetor base gasket is the first major fault I’ve found!
Yesterday, I cleaned the carburetor using cleaner and a brush, and also adjusted the spring for the secondary throttle plates.
After reassembling everything with the new gasket, the engine fired up quite quickly and runs beautifully.
I immediately tested the choke operation, and it seems to be working well; I also measured the timing and RPM with and without the choke, see the photos.
The timing appears very advanced 18 degrees, even though it was previously set to 10–12 degrees? although the engine runs very well