It does have a limiter - I checked it yesterday. It was set to 8500. I moved it back to 6250. I had raised it since the EFI ECU had its own limiter and I didn't want them fighting. I had forgotten to lower it when I removed the EFI. It is now at 6250. It is like a stumble. Not a complete shut down. Sounds like the engine is "burbling". It will go above the 4000, just little power and sounds like it is missing.
Here are some plugs. It is weird that when I replaced the plugs, I got them all at O'Reilly on the same day. Two boxes of four. They are all labeled as Autolite 3924s but one box had a black colored metal. The other box had a silver colored metal. ???
These are plugs 3-8 left to right. They have less than 100 miles on them. In person, they appear to be just a touch more white/gray than they look in the pictures.
Plugs 3, 4, 6
I replaced the intake gaskets after I last changed the plugs. I thought I was possibly getting some
oil in the intake. I also removed the PCV system and am just running two breathers now.