On my 2.7 /6 I am having an issue starting my engine. It makes a scary noise when cranking the starter. The engine does start after a few tries.

I have dual Weber IDA 3c that have been completely rebuilt. The engine runs fine after starting however a bit on the rich side. I have a 123ignition distributor and I am trying to figure out the correct advance curve. I know that if the ignition is too advanced you can get an issue like this. I have tried setting the advance to 2 degrees at 500rpm and 10 at 1000rpm- the sound is worse. The video is when I had the distributor set at 2 at 200rpm and 6 at 1000 which I really doubt is too advanced. Also- it was pretty cold outside- about 25f.

https://youtu.be/gBjkq23ZDrQ

Also- what kind of muffler do I have? I normally use an MK muffler but I needed something fairly quite while I am getting my car dialed in. I have been irritating my neighbors quite a bit.

It think you need to advance your timing. That noise might be the cylinder firing when the piston is already on the downstroke.

I'd try 10 to 12 degrees BTC at idle and before.

You'll know when you're too far advanced. You'll get a pop through carb and the engine will want to turn backwards.

I upped the advance to 12 degrees at idle and the noise got worse. I then decreased the advance to 6 at idle and now the engine seems pretty happy. It looks like I was just too advanced (haven't heard that statement too many times in my life).

Did you zero calibrate the distributor? Which is to say, did you use a timing light to confirm that the distributor advance and reality are matching?

So your timing is set at 6 degrees after top dead center? If so, something is wrong there. Even at idle you should be before top dead center. The flame front takes time to move across the cylinder. Like Mark suggests, verify what you think you have is actually what you do have.

Sorry, I was not clear. It is 6 degrees before tdc.