George, I was told that the CFM of the correct AFB for the 65 GS 401 was 600 CFM. Someone had replaced the carb on my GS with a newer but smaller than stock carb. I replaced that carb with an Edelbrock 750 CFM and boy did that wake up the ponies. I will see if I can find the info that was sent to me. Take care George. Bill Bailey
George, see if this chart is of help to you. CFM Venturi Diameter Bore Diameter primary secondary primary secondary -------------------------------------------------------- 400 1 1/8 1 1/4 1 7/16 1 7/16 500 1 3/16 1 1/4 1 7/16 1 11/16 575 1 1/4 1 9/16 1 9/16 1 11/16 625 1 3/16 1 9/16 1 7/16 1 11/16 750 1 7/16 1 9/16 1 11/16 1 11/16 Jim D.
What carb would be a good stock style replacement but about 750cfm?stock style meaning i can use the choke and stuff? Thanks
carb i have the carb and intake off a 65 gs i just removed to sup up the enginealso have the aircleaner and exhaust manifolds
The one big got-cha on those old carbs is the 4" diameter air cleaner base. All the 'modern' carbs are 5 1/8", as are air cleaners. The original chokes used a hot air pipe that ran through the passenger side exhaust manifold up to the carb. Some styles ran hot engine coolant instead. Both methods don't hold up well over long time, and only a concours collector guy would want them to. Somewhere in an earlier thread in the Nailhead forum, Jim Burek tells us that the Nailhead likes big carbs just like the 455s do. So I'd go with the 750 or 800 cfm Edelbrock AFB clones. Myself, if I ever get $300 that my GS doesn't find out about, am going to buy the 800 cfm AFB unit for the Rivi. Run the electric choke off the pink wire coming out of the ignition switch, its the hot one when the key is on, and doesn't go through resistance wire. I don't know about the 65 Skylark, but the Rivi has the resistance wire under the dash.
George, The 66 425s and some 66 GS Skylarks (A9 factory option) came with a Quadrajet manifold and Quadrajet. I think these were the 750 cfm version, but an 800 Quadrajet or Carter Thermoquad (1000 cfm) would bolt right up. These carbs have the larger opening and are compatible with the more common air cleaners (see the engine pictures in the motor mount thread). You could also use one of the AFB manifolds Jim Burek resizes to fit the Holley square bore carbs. Plenty of options here. Cheryl
George I ran a 750 cfm carter afb and it never came alive until I had it dyno jetted. Ended up with 4 different jet sizes,but it came on strong and produced 27hp more. just passing on food for thought. Jim D.
so if i switch to a carter afb 750 it will fit right in?how are those carter super competition series carbs? Thanks
They are as close to a direct fit as you will find I think. The choke is a manual setup,but I think a electric choke could be installed. The 750 is from the competition series. As in my last post I had to have mine reworked .Maybe yours would work fine. hope this helps. Jim D.
George The biggest thing was the jetting and metering rods . I had this done at a speed shop with a dyno. they never passed 4000rpm during the change and the engine made another 27 hp ... You will have to drill a hole for the Buick linkage (mounting the ball). Nothing big at all. I ran 3.73 gears and smoked a lot of 396 & 440's in the 60s &70s. A Nailhead is a sleeper, most think a Buick won't run. We have taught a few different. Not on the subject,but I did use 1.94 intakes, plus a lil porting. Every little bit helps. Jim D.
