I thought I would share a problem I had that I have never seen before.
My 72 240z with 3 screw carbs was running perfectly. With the floats really well adjusted using the 10mm method, the carbs with SM needles run great at about 2.5-2.75 turns down on the mixture screw. With Colortune, idle is a touch rich while 3k rpm is nice and blue.
I had been fiddling around with and testing out a lot of little things including fuel pump, some heat shielding around the carb float bowls, fuel pressure gauge, fuel pressure regulator, etc.
Suddenly when out on a drive I noticed that the engine was running out of oomph at 4500 rpm. I went on with my other projects but kept trying to figure out what was going on with this symptom. It got worse though and I started noticing it at all rpms. Just felt like fuel starvation. I felt really good about ignition because I had recently changed to Petronix elect ignition and coil and had tested successfully after. Was getting good spark. Finally, I decided to pull the air cleaner and look at carb adjustment. When I did this, I noticed that the front carb fuel hose from float body to nozzle was crimped some. It wasn't closed shut but was visibly crimped into a kind of drastic angle. I thought...no way that is the problem. But, I had an extra new ZTherapy hose and swapped. Started up and runs perfect.
So, the crimped hose was enough to starve the front carb bowl. How did it happen? I am guessing that sometime when I removed the air cleaner backing plate I reinstalled and crimped the hose somehow. Hard to say. Will probably never know.
Just thought I would share in case someone else is struggling with similar symptoms and by some chance this solves the problem.