And Mr Gasket 56A for top of intake/bottom of adapter
https://cimg9.ibsrv.net/gimg/www.off...0bad8c7222.jpg

Spreadbore uses the 'inner holes'. See your carb adapter (below) and intake

Inner holes hold down the adapter to the intake and the outers to the carburetor.

Thank you! I have both the gaskets I will just have to get some new studs/bolts to put it together that way.

Doing some quick searching, i see there is actually someone now that makes a spreadbore gasket with the squarebore mounting holes. Don’t know if a quality gasket or not.
https://www.summitracing.com/parts/s...iABEgLF_PD_BwE

https://cimg2.ibsrv.net/gimg/www.off...0958e02dd.jpeg

Doing some quick searching, i see there is actually someone now that makes a spreadbore gasket with the squarebore mounting holes. Don’t know if a quality gasket or not.
https://www.summitracing.com/parts/s...iABEgLF_PD_BwE

https://cimg2.ibsrv.net/gimg/www.off...0958e02dd.jpeg

Btw: threads on the intake’s carb hold down holes are 5/16-18.

Be careful with all these small parts near top of intake. Dropping something in motor would suck.

Ran great and idled perfect with another holley 850, with about 12 in hg of vacuum at idle.

So it is definitely a carb issue. I'm most likely going to tear both carbs down side by side to compare/contrast and find the issue.

https://cimg2.ibsrv.net/gimg/www.off...fa57986c0f.jpg

Don't! Save yourself the grief. Get a new carb. Carbs occasionally just DIE a sudden DEATH for absolutely no seeable reason. Honestly you've been through so much tinkering that you've found the issue and the absolute cause. Be happy you've got the fix.

Was once involved with an IHRA multi time record holder. All of a sudden it wouldn't run for ****. The carb just died. Nothing we could find or fix. But was definitely the carb.

^^^That’s a little extreme for this stage, don’t you think ?

I rebuild , say, 2-10 carbs a year. I only had one that way. I was around 17-18 old. That was around 1988. Lol.

If rebuilding it doesn’t work, then, by sll means.

Gasket kit with new power valve and needle/seats. Can of carb cleaner with red nozzle. Air gun from compressor. Wallah.

When you fo so, Don’t forget cleaning out air bleeds holes top of carb. Spray and blow thru them several times. With idle mixture screws out.

I think I found the problem. The wrong gasket was used between the carb body and base.

Correct gasket:

https://cimg0.ibsrv.net/gimg/www.off...1b236bb958.jpg

Incorrect gasket:

https://cimg2.ibsrv.net/gimg/www.off...d9ddc8adb2.jpg