You're running the Weber 38, yes? Not sure how much this would apply, since I'm running the 32/36, but same principal I would assume.

1. Make sure the fuel/air screw is set correctly. If you bought your carb new, this should be covered in the installation instructions. From what I remember, you have to start with the screw being so many turns out, then with the car at operating temp, turn the screw in until the motor starts running rough, then back it out like a half turn or something like that. That will get you in the ball park.

2. Adjust the idle set screw. On my 32/36, it would diesel at anything above 700 rpms. After you set the fuel/air screw, adjust the idle so it's just a tad above the second line on the tach. Any higher and mine usually would diesel, any lower and the steering wheel would shake at idle. That should get you close, maybe within 1/4 to 1/8 turn on the idle screw. Also, I've learned to use mid-grade gas, that helped a lot with my dieseling issue.

Good luck!