I have a bone stock ZZ4 crate engine in a 65 Vette driving a 5-speed trans and 4:11 rear end.
I have tried a 600 cfm Edelbrock,650 mechanical Demon and a 700 cfm mechanical Holley all ran very rich and just blacken the plugs and oil.  I have tried everything different plugs, timing, bigger coil, added a fuel pressure regulator set to 5 psi,different plug gaps, different power valves, jetting down, differnt air filters, float settings, carb adjustments, springs, needles and more.  I still have a very rich conidtion.  It just seems like there is not enough adjustability in the carbs I have tried.  Has anyone have any possitive experience with a Quick Fuel carb.  Will they provide the adjustability I'm looking for?  HELP!!!  

theres lots of adjustability with those carbs,just that something is being missed.650 demon should work beauty on that motor.how tall an air cleaner r u using?  

Because of hood clearance problems I have a 2 inch X 10 inch round air filter rated at 1000 CFM.  I have tried running the engine for a short period w/o any air cleaner, it made no difference - very rich.  

do compression check and leakdown check
how healthy is the mechanical side....original???  

I second that!  how old is the ZZ4?  whats your timing?  what jets are you running?   We are running 750 demons on out of the box ZZ4's and they run fine.  

The engine is 5 years old it has 5500 miles on it. Compression is within spec,timing is 36 degrees BTC @ 3000 rpm  I currently have a 700 CFM Mechanical Holley on the engine with the jets that came with the carb.  Earlier in the year I jetted down 2 sizes on the primary and I had to remove them due to loss of power.  

I had a ZZ3 that worked reasonably well on a 750 Vac. I used a demom on it also and it was rich also. Most Demons I have seen are rich out of the box. If your jetting down the primaries to get the part throttle in line I wouldn't worry about WOT until you get part throttle leaned out. Then you can open up the Power valve channel restricters to get the WOT AFR back in line. If you are going to look at a carb with more adjustability you mat also want to look at a wide band O2 sensor. I use a Innovate LM-1 that works great. I data log TPS, Map, fuel preesure and tranny pressure. On my 750 Speed demon I reduced the primary jet from 76 out of the box to 69 to get the cruise AFR to the low 15's. They have a Forum you can go to and see what other people are doing.  

take a look at www.bob2000.com "carb tuning the scientific way". helped me out big time  

Ranchand:
I have a bone stock ZZ4 crate engine in a 65 Vette driving a 5-speed trans and 4:11 rear end.
I have tried a 600 cfm Edelbrock,650 mechanical Demon and a 700 cfm mechanical Holley all ran very rich and just blacken the plugs and oil.  I have tried everything different plugs, timing, bigger coil, added a fuel pressure regulator set to 5 psi,different plug gaps, different power valves, jetting down, differnt air filters, float settings, carb adjustments, springs, needles and more.  I still have a very rich conidtion.  It just seems like there is not enough adjustability in the carbs I have tried.  Has anyone have any possitive experience with a Quick Fuel carb.  Will they provide the adjustability I'm looking for?  HELP!!!

I had the same issues with a Holley 750 on my ZZ4 in a 71 Monte Carlo. Switched to a 670 Street Avenger and picked up .09 ETA  and 2 mph in  1/4 with no other changes. Plus it no longer runs so rich.  

As a 30 year Chevy man. I have come to the conclusion there are two carbs that do best on Chevrolets. Years ago when GM came out with the Quadrajet, I fell in love with it. It was fast, but yet if yo stayed out of the back two barrels you fuel economy was great. However, only 1 out of ten were worth a dam. So I went with the Holly Quad replacement 500 CFM. Bolted right on. Picked up ET's at the track. Come to find out GM over carbed the small blocks from the factory. Then I found the Holly 1850 with Vacuum secondary. Fell in love with it. I started running circle track and it was the only carb we could run. We couldn't run a jet plate in the rear so I drilled out the jet holes......The they let us run them. That carb was the ticket. I can take it  part......put it back together.....re jet it.....Build power.....the hole nine yards Love the Carb. Then I read that Elebrock bought out Quadrajet. And fixed every trouble that ever happened when GM had it. Bought one for my 70 Monte Carlo.....Love it.....Bought one for my 84 K5 Blazer...Love it.....Bought one for my 69 Pick up....Love it....It is the bomb.......Summit sells them for all applications   try it you will like it


I hope this helps