[Bentley]

Has the motor ever been rebuilt or how long since it was??

 

[Bentley]

You may have more than one issue. 1st did this just start or was it after the car sat for some time? Good chance the carb needs a rebuild, especially if you have been running ethanol gas. You could have a stuck float, a damaged needle valve, a blown power valve etc. all would cause flooding conditions.

I would also suggest you post this over in the Vintage Mustang Forum. There are some real experts on the 60s engines there.

How old is the oil? Over time it is normal to get dark, but if it happens quickly it could mean the engine is ready for a rebuild and the rings are leaking. You need to start with some basic diagnostics.

1. Vacuum check
2. Compression Check

These will help identify the condition of the engine. If it checks out OK, then you need to look at rebuilding the carb and doing a tune up.

All good ideas..... Simple things first
Check for moisture under the distributor cap or if any of your spark plug wires have gone bad or have rubbed through.. If your not firing correctly, unfired gas will by pass your piston/rings......
How many miles on your engine?? My first thought was timing chain/gears?????
Pull your dipstick and smell the oil.... If it smells like gasoline, change it before you try to start it again...