So I did a search and found ALOT of info on 8ba and 59ab setups. My question delves into the wonder world of my '37 21 stud! This motor ran great with a single carb on a regular dual offy intake with the rear carb plated off. This year I want to get both carbs going. I will be adding an electric fuel pump and a regulator. This is the rundown..should I change anything first or just go with what i got? engine: '37 21 stud bored .040 over stock cam original divebell dizzy with vac brake converted to 12v aluminum heads milled .030 carbs: offenhauser reg dual intake with 2" carb spacers 2 rebuilt 7RT ford 94s 51 jets all around blocked power valves(both) one is set up for primary with choke other is not I ran the carb with a velocity stack and screen(no filter) I live AT sea level and rarely drive at any significant elevation. I guess my main concern is matching PVs and jets to my needs. Im rather green at fine tuning carbs, apparently Ive just always been lucky. Thanks again for any info!
Ok what are you asking? Did you try running this setup yet? I think your going to find your jets too rich and you might want to put power valves in, but smaller than stock will be required with the holley's. I also like to run the choke on both carbs with them sync'ed together but I've seen plenty run like yours also. Lots of it is trial and error to see what setup your motor likes best.
Distributor tip: Look at the rear of the shaft. It will say either "68" or '11A" back there... Find an 11A shaft and advance if you don't have one. Significant upgrade.
The main thing I'm wondering is if you want to run progressive or not. Progressive would probably be the way to go..
Stud, this is a pair of matched carbs that are new rebuilds that havent been run. Basically, If im waaay of Id like to know now while everything is more manageable. Bruce, is this stamping on the "key" if you will? I will look now but I thought I saw a number and letter once. Ill be back in five or fewer!
If you run with pv's I think you would run 3.5s in both totaling 7. Correct me if I'm wrong... Interested in your results. I have about the same engine setup with a single on it and was thinking of going with a 2 94's.
I would start with 7's. Check out this post guys, it has some really good info about setup. http://www.jalopyjournal.com/forum/showthread.php?t=36751
PV number represents vac level of opening, not the restriction. PV is an on/off valve for gas that is actually metered in the carb body.
Ive read in a few different places that with a regular dual intake progressive linkages will create idling and vacuum issues?!? Do rocket scientists have to take "carburetor 101" as a core requirement??
They can if setup wrong. The thing about setting up a progressive setup is to ensure the secondary carb is exactly that. The trick on is making sure that the throttle valves seal tight, the linkage performs with zero binding and returns to close all the way and seal tight. That carb can be blocked on the pv and idle circuits, as it's job is only to boost when you open it up. On the primary I would run the 7.5 PV and 51 jets to start... That's at least where I would start myself.. Though weird things happen when setting up carbs. I was sure I was gonna have to go progressive on my 4x2 caddy setup. Right now I'm at 3.5 PV's and 48 jets all the way around with straight linkage. It runs great.
If your running a non-progressive dual carb setup wouldn't your vacuum be decreased a bunch by having another big hole in the intake (the 2nd carb)?
That's the reason for going to a lower vac number to signal the opening...when 2 carbs start to open the vac drops off much faster than with a stock single, so lowering the tip in vac is a way to get PV to stay closed until it is needed at close to full throttle. It's pretty much a try-and-see to get right level.
I dunno if I'm saying this right..The vacuum isn't decreased, but the rate of vacuum decrease is changed... Does that make sense? So even though you're doubling the number of carbs..doesn't necessarily mean you need to 1/2 the PV.. more like decrease the point where it opens so that it doesn't come on too early. With straight linkage dual carbs maybe start with 5.5's and go from there..
So if your running a duals with straight linkage and 7.5 pv's, would they even open up? Then with 51 jets you'd be running rich at idle and just right on acceleration? Definitely a trial and error project. :]'
Yes that makes sense. Dreddy the progressive seems like a good way to do it, but what about starving cylinders opposite the main carb at idle and low throttle?
Saxon has it...as I said, vac drops faster due to more area opening. It would drop past the stock PV level around 8 very fast and get you driving while at part throttle or cruise with PV's open. The lower number, like 3.5, does not open til vac reaches that level so would come in later, which is what you want. Power enrichment is only wanted at high throttle openings, not at cruise or in slower acceleration. Vac would drop past 7.5 probably way too soon. High vac (above the number of rating) holds valve shut, it opens when throttles open enough to drop vac below the number of the rating. Opening too early hurts performance and can kill the rings from richness, not opening will kill off performance at full blast.
Worth buying a vacuum gauge and seeing what your particular engine develops at cruise or gentle accelleration. (Already responded on Fordbarn)
Well Bruce I was saying they wouldn't open when I should have said they would open to quickly. Thank you. Sometimes I'm a little thick.
Hey Mart, someone responded after you did over there. Great info, vacuum gauge ordered. Can't believe I don't have one already :[
Thats why they call it "tuning". The power valve number depends on the manifold vacuum. The 94 carbs only flow about 185 cfms. You can run them together with no problems. Match the PV's around 4.5 and jets around 52-55. After the setup make a power run with new plugs, shut off the engine and coast. Inspect for a dark gray color, light or near black color will indicate a jet change. If the power valves kick in too soon it will bog, too late and it will hesitate. With both carbs hooked up and running use a vacuum gauge at idle, rule of thumb is to use 1/2 the number for your power valve number -1 (vacuum at 15 use a 6.5 PV). This will give you a start as the cam and distributor advance will make a difference on the opening. Use Dick's power valve gasket.
I did pretty much like Ricks Garage said on my 2X2 and it runs great. I used a vacuum gage to estimate where I did my normal driving and where I wanted to power valves to tip in. Because my engine is modified quite a bit I ended up with 55 jets The engine had a tendency to run hot on a grade untill I went up to 55 jets.
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