Spark plugs 3 and 4 fouling at idle on my 240z

[jalexquijano]

I recently carried out a compression test on my 240z engine and the result was perfect. Nevertheless, last sunday i left the car idling with the Hood open for 10 to 12 minutes and the engine started to idle roughly. I then decided to drive the car and the engine started missing at 2nd and 3rd gear. Surprise, when i got home i pulled spark plug 3 and 4 and both were black fouled. The other ones looks okay.  If i already changed the spark plug wires, cap and rotor and the compression is good what could be causing this? Should i use some nose pliers to tighten the terminals?

[datzenmike]

Dual SUs? Or side drafts?

 

Side drafts the middle carb float is stuck or for what ever reason it's flooding, or jet backed off/fell out or has the wrong jets in it.

 

Dual Hitachi SUs probably the intake valve guide seals are bad and burning oil.

[yenpit]

Fuel fouled or oil fouled?  Fuel fouled, likely a carb issue like datzenmike says, but relatively easy fix, depending on what carbs you have.  Oil fouled would be much worse news, but valve stem seals would be your first hope, broken piston rings would NOT!