Hi Can Anybody Tell Me Why My 260z Will Start And Run Excellant For 20 Min Or So And Then It Starts Sounding Like Its Running On 5 Cylinders. I Will Limp It Home And Then After It Sits For A While, Ill Go Back Out And It Fires Right Up And Sounds Normal, Then Ill Try It Again And Same Thing Runs Good For Awhile And Then Back To The 5 Cylinder Sound And Running Crappy.i Have All Original Carbs, That Seem To Run Excellant, Until The Car Is In Its 5 Cylinder Mode..

I had same problem years ago but with a different car,turned out to be my ignition coil

I had a problem like that with my 240Z lately....she would run great for awhile and then start running like crap like not getting enough gas to the carbs. I thought it was the fuel pump but turned out to be the gas tank....apparently alot of crud had built up in there over the years. They had to pull the gas tank, clean it and resurface it, etc. Runs great now!

Could be a coil going out , or could be a fuel filter clogged and the engine is starving for fuel. What ignition are you using ? Sometimes when the things like coils and even spark plug wires get warm or hot they can fail.

^ya, i remember on my grey Z that i kept trying to troubleshoot a fuel problem. then i replaced my distributor with an E12 280zx dist and my car ran wonderful!