I'm not much of a mechanic,so forgive me if I say something stupid. I am refreshing a 73 240Z that I have owned since high school(25+ years). Back in the early 80's,I replaced the flat tops with 72 round tops that I purchased from a salvage yard. They worked well for years, but now the car has been parked for 10+ years (body rust issues). During the refreshing, I have considered switching to a 4 barrel Holley setup rather than trying to rebuild the round tops. Any comments or suggestions would be appreciated.

The consesus here will be to rebuild the round tops or get a set from Z Therapy. The Holley conversion has been discussed many times here and the general opinion is that it doesn't work well on an inline 6 cylinder eingine. There was a 'tuner' type episode on one of the cable channels where they took two 240z's, converted them to Holley 4bbls and they actually ran slower in the 1/4 mile than the stock setup.

.... Stephen said, a set of SUs (HITACHIS) that are refurbished to square one will yield the easiest set of carbs to keep up with, going. Worn out, they are a pain to keep tuned, but refeshed, no trick keeping them dialed in.

And as a final point, $600 for a set of ZTherapy rebuilts is probably cheaper than a new Holley and the required manifold. Cheaper, and much easier to set up, as you'll be starting from scratch on the Holley, whereas the SUs will be ready for fine-tuning and that's all.

.... Stephen said, a set of SUs (HITACHIS) that are refurbished to square one will yield the easiest set of carbs to keep up with, going. Worn out, they are a pain to keep tuned, but refeshed, no trick keeping them dialed in.

agreed! since dealing with SUs, downdraught carbs look like a rubik's cube

I understand downdraughts. They work fine on what they're designed for.

4 bbls are too rich in mixture.