spark plug smashed in?
 

got a 73 240z with the l24 and triple webers. changed the spark plugs last night and found that the number 6 spark plug was smashed in and also very wet. im still trying to get the carbs dialed in and the timing was done by ear. the car runs good at idle but sputters and backfires a lot when you get on it.

By "smashed in" do you mean the tip has been pushed down onto the electrode?

This could have been done by accident when installing the plug. It would be a pretty clumsy accident but it does happen. It would be wet as with no spark, the fuel isn't being burned.

Get a new plug (preferred) or regap this one if you can, carefully reinstall, run the car for just a little bit. Note if the behavior improves. Either way, pull the plug and recheck the gap. You want to make sure it's not the piston smacking the plug. That would indicate some serious internal damage.

If it got "smashed" in, I'd say there was a foreign object dropped into the cylinder... in which case your piston and head chamber probably look like hamburger meat.

Yeah, that's one of the worst case scenarios. Unfortunately OP hasn't come back to say what's been found.