Hey guys, our shop is installing what looks to be a stock build v12 into a 1937 studebaker truck. The owner hooked up the 3-97s without a progressive linkage so they are all direct hook up. Will this be ok to run? Also, when it comes time to hook up the choke, should I only hook up the center carb choke and leave the other 2 alone? Thanks!
I'm not going to say I have the definitive answer to your question. What I will say is I don't see why it wouldn't, rather shouldn't work that way. In theory if not in practice, old truck, push down the pedal, pull the choke, crank engine. I'd look at the way things are set up and ask why it works that way and what prevents it from working so. How To Start a car or truck with a Manual Choke, lastchanceautorestore.com - YouTube Installing A Manual Or Electric Choke On A Holley Carburetor - YouTube Now I have to say, I'm the idiot. Broke idiot at that. First thing I did was count plug wires to confirm it. Then I counted carbs. That was followed by the mumble, lucky bastard. Setting the stage for my expertise, I've arm chaired, played only with pairs, never touched a triple threat. Recently however, I got the thrill of watching the fine folks at J&G Urethanes decanter from a 45 gal. drum into 7 - 5 gal. pails for me. I mention that because the original plan was to get one of the guys to hand pump it out. Good in theory but if like those carbs with a stroke they blob, blob,blob, it's a problem. Plan "b" was the working model, tilt the barrel pour from a spigot. I recall something about fuel atomization in that kind of set up. Something about distance. I mention that because, well it's three carbs on a log and where they sit makes you wonder who's getting more and who's getting less of it. Guys have found all kind of ways to make "it" work. Making it work, takes a little longer. DOUG & THE SLUGS - Makin' It Work - YouTube Making "them" work, that's the hard part and questionable. Remember this is me, I know nothing, but I always wondered if it had to be so hard. Times like this I think Triumph, I tickled both carbs not just one. Three would have been an extra to tickle, I guess. That's where I'd stand on it. And for that to work, the lifting on the needle off the seat in relation to the allowance of fuel to flow past has to work in harmony and not be broken with progressive additions from the other carbs. Maybe I'm not the guy to listen to here. But hey, it's a popular thing to have a couple carbs that don't do much. Guess the one closest to the middle will be the one that works? Making it work. I don't know. Try it and let us know the results. But if I was going to ask another dumb question, it would be who decides the length of the arm for the linkage? Seems to me that's a factor in lifting that needle off the seat that seems to be missing in these conversations. Maybe it doesn't matter? Or maybe it does. I don't know.
chokes are nice for the cold starts and after sitting a while, but not really needed. If a good electric pump is installed as a "pusher" (assuming this engine has a mech. pump) a couple of pumps on the carbs ought to start it. A single choke might do it on the center, maybe. I'd try to run it with all three and see how it performs, then maybe block off the end two and try just one. One thing you might consider is the fuel pressure, don't know about those carbs but 3-4 psi seems to be good for most multi applications. Multi's ain't for the faint of heart.
You will only need a choke on one carb. If I had a choice I’d pick the center carb but not necessary. I think three may run well with straight linkage on a 12 cylinder. You may have to play with the power valve and jet size. I’d stay on the lower than average size range for starters. Get yourself a carb synchronizer and know how to use it. Many do not.
It appears all three carbs have idle circuit adjustment screws. To get it to run right you need to synchronize the carbs using a tool like this. In order to successfully run progressive linkage the two end carbs shouldn't have idle circuits and the throttle plates need to seal when the throttle is closed.
Progressive linkage will solve many problems! I would consider this, if possible. With straight linkage, all carbs will be opened at the same time. You could maybe set that linkage to where the two end carbs are completely closed at idle, then the center carb choke will work good. This may not let the two end carbs open 100%! If all carbs are used at idle, the choke will be less effective. Just my two cents! Bones
If All the carbs are hooked together Non-Progressive, and you choke only One Carb, then when the Choke is Applied the Fast Idle Cam is gonna Hold the Other Two Carbs Open also.
In my opinion, and it's just an opinion, For one choke to work properly you need to run progressive linkage. If not, when the engine is cold, and during warm up, if you open the throttle without chokes on the secondaries it's going to be too lean way to quick. It would likely be just fine after warm up, but a bit persnickety (at best) until reaching operating temp. Personally, with three carbs I'd run a progressive linkage, but my part of the world is colder than yours. I run 3 deuces on my 390 Galaxie with progressive linkage and 1 choke. It works very well. I'm in the throws of putting dual 94s on my '50 Flathead Ford with straight linkage. It will have both chokes working.
There, in lies the rub. The making it work part. I'm sure I could be wrong here but, fuel pressure is rarely the issue. Think of it this way, tilt your head and I'll pour it in your mouth. Swallowing it, that's the hard part. If you give consideration to the engine, it has to spin quick enough to draw in a gulp, and not choke on the amount it draws compressing waiting for a spark. Cam, lift and duration, what about that elephant in the equation. I'm all for syncing carbs, but... 1 big gulp = 3 big gulps. Maybe what's needed is not big gulps but 3 steady sippers. But if you give it any thought at all, a single needle and seat. That's not a complicated thing. Two of them lifting at the same time, not much harder to grasp. Why should 3, or 6 for that matter make a difference? My opinion is they don't, what does is the volume of gas allowed to pass in relation to the needle being lifted. And with movement of the arm, the amount of lift. Lastly, the size of the straw and the amount of the draw. How to Build a Tri-Power / 6 Pack / 3 Deuce Carburetor Setup - Stacey David's Gearz S2 E5 - YouTube My opinion seemingly a theory shot to hell, maybe, maybe not. According to this, shot somewhat to hell. Then again... (not my picture) I could be right in theory just wrong in application.
If two ‘97’s - fixed linkage, is ideal for a ordinary flathead, would not 3 ( fixed linkage ), be more correct for a V12. After all, they are a tiny little carb. - ( just look at the above photos……..) Chokes in all is how I would do it, unless you go progressive. Others will disagree. If progressive, choke in primary/primary’s only, although you should leave chokes in place in secondary, even if not hooked up, - (so I have read on here).
Multiple carb systems. I can't afford them. But I'd sure like to try setting one up. How To Set Up Multiple Carburetors on a Vintage Engine (speedwaymotors.com) - If you try to use three primary carburetors, it will be difficult for each one to get a proper vacuum signal or supply the correct air/fuel mixture. This causes the engine to load up at idle and foul plugs. I'm not sure how to interpret that past, maybe the problem isn't that each are primary carbs. Engine Performance Testing with a Vacuum Gauge | Actron -Each of these has a characteristic effect on vacuum and you have to judge their performance as compared to what is considered "normal". I have to admit I'm a learner who understands it better when I have a solid to make sense of the explanation why. A while back it was a SBC with a 3x2, Pertronix and a backfire. How To Tune Carburetors, Step By Step | Cycle World -Such work consumes a lot of plugs, so you may want to clean them for reuse as suggested to me years ago by “the Champion man,” Bobby Strahlman: oven cleaner, followed by a water rinse. I might have to start a Go Fund Me page to get me one. But good luck with it. Looks like fun.
Put a progressive linkage on it, unless you plan to do drag racing. Only the middle carb gets a choke - treat the other carbs like secondaries, so no choke, disable the power valves and idle mixture screws. You are idling only on the center carb.
It's easier to get all three working as one unit then is to get two sealed off and made into outer progressive dump carburetors. Start with each setting the same on all three, float, needle hight, mixture, throttle opening, what ever you have to set, do it three times. Once the engine is running, adjust each one the same. An Air/Fuel ratio gauge would be real handy to have for this along with the Uny-Sinc gauge. Once you have it running correctly, hook up the linkage, be sure take and slack out of the linkage so all three move at the same time. You will get a much better fuel distribution with all three work as one.
You only need one choke on the center carb IF your linkage was progressive. But only choking one carb with non progressive linkage defeats the purpose, and might as well not have any chokes hooked up.
I like to idle on all three and run on the center. The throttle shaft to base should leak very little on all three. A UniSyn definitely helps and what JoeH suggested, one at a time with plates is an excellant idea. These are not early Ford carbs but work perfect progressive.
I'd like to think as a guy understands more, he will find solutions to greater problems. Those Holly's look good on there. Like they belong. Not paying attention at the back of the class, what size is the six? I was curious the breathing capacity. It's ability to draw air, bore and stroke. 3x2 makes sense on a six but seems slightly off on an 8. On the 12 it looked good. Must be a math thing. But it looks spot on there. Balanced, in proportion. But that linkage. When I think progressive, I'm not seeing it. Looks to me to be in unison. One movement moves it all. But it looks great. No doubt about that.
I think, and it's hard to see in the picture, that the linkage from the center carb to each secondary carb has a slide that doesn't engage until part way through the throttle travel. That's the way my Holley triples are set up, as the primary opens, the linkage takes up the movement in the slides and then opens the secondaries.
The GMC is 311” 10-1 compression, a reasonable Howard Cam and head work by Mike Kirby; 1.94 intakes and 1.60” exhaust. The carbs are Holley 1960 Mercury 292” and rated at 280 cfm and were used for 20 years on a Clifford manifold. “Center of the Galaxie” has it. If you expand the photo the front carb slider is evident. The rear carb slider is actually on the center carb closest to the factor arm linkage. Much of it is from Ford FE’s and some I made. The main actuator on the back of the rear carb is the center crossover arm on an FE dual quad 427 all fed by a cable foot feed. Not my first multi carb set up but definitely my most challenging. The car was my first LSR in 1975, it set many Bonneville and El Mirage records and I gave it to my son 4 years ago and included this engine.
There it is alright, and I did see it, it just looked like it was in a fixed position. You're saying it slides. Crystal clear. I'll take your word on it that it works the way you say. You have me convinced that if I every experiment with 3x2, it's going to be on a GM six.
That’s an early photo during the build even tho it had been run. The rod going to the rear carb does have the same slot and was adjusted later to have the same gap as the front so it would be more evident. You would think the slot would be at the rear carb but it fit better in the opposite direction.
This just in from the "let's not overthink" dept, and assuming the manifold itself feeds all 12 as one unit. Having just 1 choke will be fine as it will add just a smidge of extra fuel to the manifold, and conversely all 12 cyls. Is there a heat riser? Bet not under all 3 if there is so how does that help? Likely blocked. Fast idle cam, adjust it. Does the full choke demand a full opening to fast idle on all 3? Why not reduce it a bit to where it's just a small amount of throttle opening and ONLY at full choke. Will it run all 3 working all the time in an efficient manner? If jetting and settings are right, yes. BETTER if set right because 4 cylinders each get their own carb. And blocking 2 to set 1? I'd guess that's best for progressive linkage efforts. The manifold's engineered commonality for all 12 will disturb setting up 3 separate 4cyl engines. Ok, I get it, seems like overthink with all the above verbiage but I had to get there from here somehow. 1 shaft, all 3 the same operating position, common plenum, jet it and forget it. Choke? Reduce the high idle throttle position so the other 2 don't add too much air on cold start, or indeed remove the high idle on full choke. You're gonna shove it back open some as soon as it fires anyways. All these old engines have a "secret handshake" to be learned getting em started. These are general inputs, I'm not there and don't really know enuff particulars to go much deeper.
A choke shuts off/ restricts the air flow above the venturies , so the the pressure drops around the Venturis and the atmosphere pushes the fuel into the venturies and into the engine. Unless you some how “ shut off” the outside carburetors there will be no reduction in pressure in the middle carburetor, because the air will flow into the engine via the outer carburetors if you have straight linkage and idle on all three. There will be “some” choking effects, due to the limited restrictions of the outside carbs plates being almost closed. But it will not be the same choking effect as with only one carb. May be enough to get the engine started…..maybe not. Just my opinion. Bones
Hello, That looks to be a lot of carburetors for a Flathead to run all at the same time. If the throttle linkage can be adjusted to a progressive set up, it would work better for your Flathead, what ever the size and power. A simple start with the center carb, then when you want a 4 barrel carb to kick in for more power, the linkage will do the job. Our situation with the 3 two barrels on our 1958 348 motor of the Impala was vacuum powered. The center carb did all of the hard work to start smoothly every time, run 75% of the time and not waste a ton of gas during the daily drives to school or local cruising activities. But, when we wanted some additional power of the other two friends, all it needed was to push down on the gas pedal for a smooth running three carburetor set up. But, for what it is/was worth, after the black vacuum tube fell off and we only had the use of the center two barrel carb for a full quarter mile, it was obviously lacking additional support from the other two carbs. So, we installed what was called progressive linkage. Jnaki The “progressive” linkage was nice looking, seemed to function well and when we did the trial and error tests, came up with several problems we did not like. As much adjusting we did, the center carb did all of the work. But the linkage stopping points left a lot to be desired. When all three were supposed to be wide open for the full effect of three carbs. It was fine. But, the everyday throttle was limited. It was just the way the progressive stops were adjusted. When the every day center carb was adjusted to run full open, the outside two carbs were not fully opened. It did not matter how minute the adjustments were, the carbs with the progressive linkage just did not make normal driving around pleasant. And there was no need to have all three two barrel carbs running for every day normal stop and go driving to high school or to the beach. The 348 had the extra power to run all three carbs at the same time, but why? It was not Lion’s Dragstrip starting line everyday and it just was not the right way to run any motor. Add a situation that instantly got the blood running, a full throttle jam heading for a dead end and cross street was bone shaking. And within the following week, the progressive linkage was given to a friend, with the warning, “can be jammed at full throttle at any time.” The black vacuum tube got the clamp on and the whole thing was back to full race, if and when needed. But, the cruising around speeds and throttle was perfect up to a certain point, when the other two sleepy guys on either side decided to participate for full power of the modified 348 Chevy motor. Fast is fast, although everyday fun is the main reason we all had our modified hot rods during our teenage days of cruising and racing… YRMV
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