I installed a 750 CFM Edlebrock on my 58 Buick Special in 2021, but havent ever managed to get it to run right. It has the original 364 nailhead. Which was re built 10 years ago, and re bored to 0.40, with original points based distributor. Despite setting the timing up correctly, its running lumpy, and has a flat spot when the throttle is only part way open, more so when under driving conditions, plus its running rich, despite the idle mixture screws only being opened one complete turn. I'm wondering if 750 is too large for the 364, and also if changing the jets and meetering rods would help? I'm starting to piss my neighbours off now with messing about trying to get it running properly. I'm running the engine through a set of lake pipes.
Patrick is right...not the CFM it's the Edlebrock. Very common issue with those carbs, especially with Buick's.
Yeah, I would like to know this too, and what would be an ideal carb to use, I would ideally be looking for something I can buy new that would bolt straight on with little fuss, I have messed about with 2nd hand carbs in the past with mixed results. Fed up of trying to get an old piece of **** to work.
There no such thing as a carburetor that is right for any engine right out of the box. Edelbrock and Holley are no exception. They come calibrated to run acceptable on most engines, but they are nowhere near to optimal. They ALL require tuning. They are used because most just want it to run halfway decent, and they do. You want better, tune it. They are much easier to tune than a Quadrajet, but a Quadrajet is a superior carburetor. The Quadrajet was calibrated for the engine line it was meant for. What happens most times is guys think they are all the same, so they'll plop a a QJ meant for a 1980 305 Chevy on to the fire breathing big block whatever, and when it doesn't run correctly, they blame the whole line of carburetors. In any case, buy a tuning kit for it. It's a Carter AFB clone. Buy a book on tuning them, and experiment to see if you can get it running better. Also, people have a common misconception about idle mix screws. They don't set the idle mixture, they set the volume of air fuel allowed past the idle ports into the air flow. The actual idle mixture is set by passageways in the idle system, air bleeds and such. If it is running rich at idle, it may not be the carburetor calibration at all. A common problem with Quadrajets is called nozzle drip. The primary side of the QJ is so efficient that it does not take much to initiate fuel from the primary nozzles. If you open the primary blades too much, the engine starts to run on the main system, instead of the idle system. Pretty common on the QJ, but it can happen to other carburetors as well. The classic symptom is an extremely rich, eye tearing exhaust at idle. The mixture screws become unresponsive. Try closing the idle mixture needles. You should be able to stall the engine. If not, the engine is getting fuel from somewhere else. (mains) In a lot of cases the idle ignition timing is lacking, so the idle speed screw has to be turned in more to get an acceptable idle speed. That leads to the above problem. With a Nailhead, chances are your initial timing is very low single digits. Vacuum advance should be connected to manifold vacuum. That will advance idle timing and allow you to back out the idle speed screw and close the throttle blades.
I’m add .50 to Larry’s $100 post: Parts store and online sourced remanufactured Qjets are assembly line, mix and match, hammered together crap from often worn out or damaged cores, with a useless guarantee. The new casting chinese copies are even worse. Same with AFBs. Get a good core rebuilt by someone who knows these things, not a store, not a dude and a chick with tats and flat brim hats. Patrick
Aaah ok, that makes sense, the idle mixture screws are largely unresponsive. I set the dwell angle to 30 and timing at 5 degree TDC, as sescribed in the workshop manual. The vaccum advance from the distributor i hooked to the port on the passenger side. Driver side, and PCV are blanked off. The port on the intake manifold is blanked off too. The break booster is conected to the vaccum port at the rear. Thanks for the help, I really appreciate it.
You need PCV. With the engine running, unhook the vacuum advance. If you don't hear a hiss, it's connected to a ported source. Hook it a manifold vacuum source. When you do, the idle should increase noticeably. If it doesn't, the vacuum advance canister is no good, replace it.
my only beef with the Edelbrock's are that almost everyone i worked on {maybe 8-9} they all leaked air past the throttle shafts even brand new! some worse than others. i imagine they are all made overseas with terrible tolerances. check this before you go any farther. it makes a rotten time to get the car to idle nice and clean off the idle circuit if and when they leak!! best of luck. charlie
I've been reading a bit about PCV on Nailheads, and in particular the lack of them on earlier ones, and then the need to fit baffles inside the valve covers to stop oil getting sucked out etc. Some people say they work better with just the breather style caps with the mesh in, like I currently have, some say to block the draft tube and put a PCV valve into one of the valve covers ( as far from the breather as possible, and running it to manifold vaccum, and then some suggest runing a pipe from the air cleaner to the outlet for the draft tube . So now I'm really not sure what to do. Hahaha
Stock, the PCV goes to the right valve cover. The breather is in the left valve cover. This draws air across the entire internals. In one side, out the other. There is a baffle that bolts to the two rocker arm hold down bolts in the middle is ALL you need to be completely stock appearing. I should have the CORRECT valve covers, nec grommets & other things needed for a complete stock appearance. Tom T.
I hate to say it, but the Edelbrock on my 425 was removed from a Chevy 350, placed in a plastic bag for about five years, then bolted onto the 425. At 650 CFM it's too small, but it runs well. I am thinking about putting a set of dual quads on it though - primarily for the look.
It's almost impossible to over carb. with any AFB/Edelbrock as the secondary air flap will open only as far as air demand allows. Tom T.
Aah i see. When you say right valve cover is this passenger side? And left is driver side? Do you also have the baffles? What sort of price are you asking for the parts? I'm in the U.K.
650 cfm will support 400 Hp, so if your heads are not fully ported up well then your not near that level of hp.
I wonder with a way over sized carb off idle and at a low rpm the primaries will still be too large and with out the secondaries coming in way later it will have unequal fuel distribution ? have no ideal just wondering.
