248 dual carb linkage and/or jetting setup

[Skidplate]

I have a 1937 248 engine with the later 40-41? dual carb intake/exhaust setup. I'm running Stromberg carbs with my peddle hard linked to the front carb. The rear carb is connected to the front carb with a slider rod that only engages after about a 1/4 throttle. This seems to work pretty well but I'm seeing about 100deg heat difference (via laser temp gun) just below the two carbs where the exhaust manifolds bolt to the intake manifolds with the rear manifold being the hottest. I'm at 5-7k feet elevation so have chosen to use variable jets to get my best spark plug burn and have taken great care to set all the jets the same. I haven't tried it yet but was wondering is there maybe a common knowledge that the rear carb should be jetted differently than the front. Has anyone else set up their dual carb config outside of the recommended "dual carbs should be hard connected together" or "I'm at sea level so everything works just fine with little adjustment" and how have you done yours. 

[1939_Buick]

Some owners connect in parallel so both carbs operate exactly the same.  Not as master and secondary on higher throttle.

 

1942 shop manual has info on setting.

 

Download the 1942 Buick shop manual for free. All of it section by section.

Or click the pdf link to pay.

http://www.oldcarmanualproject.com/manuals/Buick/1942/Shop Manual/

It is very comprehensive and has information that can be used with all straight 8’s.

It has more information than was included in older “Shop Manuals” before 1942

 

http://www.oldcarmanualproject.com/manuals/Buick/1942/Shop Manual/07 Engine/index1.html

Edited February 22, 2023 by 1939_Buick (see edit history)

[Lawrence Helfand]

Best setup is matching stock jetting front carbs with rear intake weighted flap removed. Twin chokes are required. Using Summit racing linkage kit to front carb and from front to rear for parallel linkage. I use two Carter 528S carbs but Strombergs work ok too, tried both and Carters were a bit better off idle. I have been using this setup for several years and works beautifully. More balanced mixture and more even heat as well as smoother idle and more power off idle as well. Gas mileage has not increased and may be a little better. Easy starting hot or cold. I also pinned my heat riser flaps in the open position for a cooler intake.  Overall its a big improvement with no downside. 

[Skidplate]

Hey thanks "39". That site rocks. I haven't tried the adjustments yet but I have much more info now. We'll see how it all translates to Strombergs that aren't specific to this engine. Wish me luck.

[Skidplate]

Yeah Lawrence my Hot Starting is awful. Didn't think of heat flaps. But I spent so much time and effort getting those looking great and working properly. Go figure. Got the Strombergs because I didn't know what else would work. Carters DO seem a little better made. Maybe I'll try those next time. And I'm only choking the rear carb mainly because my existing choke cable is too short to reach the front carb. Poor excuse but there you have it.

[Skidplate]

Ok so where is the Intake Weighted Flap? I'm assuming since the Choke Flap is at the top then the Weighted Flap is at the bottom?

[neil morse]

Yes, the flap is at the bottom, in between the manifold and the carb.

[pont35cpe]

I see your carbs are tilted forward. Could this effect your fuel level? I have a dual carb setup on my `36 Buick(have not fired it up yet), i had the manifold milled flat so the carbs are level/vertical. I am also using 2 front(Like Lawrence, Carter 528S)carbs with parallel linkage.

[Skidplate]

They do indeed tilt forward. I thought this was a little odd too but who am I to argue with over 100 year old engineers. But to be honest though,  I've never really had a good understanding of how fuel levels effect a carbs function anyway.  One would think that as long as the fuel bowl stays filled enough to NOT starve the engine of gas then all should be good. I know this couldn't be true because so much emphasis is always put on fuel level measurements but there you have it. A little ignorance certainly goes a long way. So as it stands right now the car actually runs pretty well. My gas mileage sucks at around 11mpg but if the car wasn't heavy before, it certainly is now. Between the commercial grade tires (5) that were the only thing I could find in the correct size that wasn't lame no-traction show (not snow) tires, but are heavy as hell.  And then there is the two really heavy but really comfortable heated and cooled bucket seats along with the 1/2" thick wool floor insulation. So given all that, and all the other small but compiling weight additions,  I really can't complain MUCH about it's acceleration. It wants to stumble a little in low speed turns but so far I've gotten it up to 70mph on the interstate with seemingly more throttle to spare.  At this point I'm just hoping there's some little something I've missed that others before me might know more about. And I actually DID consider doing something to correct the forward tilt of the carbs but nothing jumped out as a viable solution.

[pont35cpe]

Your `37 engine is mounted pretty much level. The `41-42 engines are tilted(lower at the back), this is why you have the tilted carbs, when mounted on a level engine.

[1939_Buick]

In 1939 and later the  engines was sloped and the intake manifold has a step. Carb base was horizontal

Image is 1938 & 1939

 

Edited February 24, 2023 by 1939_Buick (see edit history)

[Skidplate]

So you got me to thinking (thank you for that) maybe there's something to the tilt thing. I've been seeing another problem with my front carb that I think all ties in together. After I've taken it down the road for another test and tweak drive, and I pull it back in the garage to look things over, on occasion I will hear this odd little sound about every two or three seconds apart. It's happened a couple times and I've found it to be the front carb with fuel dripping from what appears to be out of the engine side lower rod of the throttle assembly onto the hot exhaust. I know, right? It's got engine fire written all over it. So I pulled the carb to see if something could be able to leak from the fuel bowl out of that lower butterfly rod. There's nothing down there but the rod. So I got to thinking what you said about machining the tops of the intake to level the carbs. I poopooed machining the intake (sorry, you were right) but I realized I CAN machine the new insulators that I just installed under both carbs. Got my angle of slope and calculated what I needed to cut. Did I mention I have a 3axis mill? Just finished the front one and I'll try it on tomorrow. Oh, and as for the later version of intake that compensates for the engine slant... it should have occurred to me before because I have one of those exact engine/intake config engines setting here on a stand. It just never clicked. 

Edited February 25, 2023 by Skidplate (see edit history)

[pont35cpe]

Even with the angled insulator, you will have to bend your 3 mounting studs, vertical.

[Skidplate]

Hope not. We'll see. I kinda tilted the carb up to see how it layed. Again, we'll see. But isn't it the same deal as yours. They didn't repunch YOUR bolt holes did they? Or did you bend yours too?

[pont35cpe]

My studs are bent vertical.

[Skidplate]

Ok so I machined the spacers/insulators and reinstalled. They actually bolted up fine. Got everything back together and test drove. I'm starting to believe that these NEW Strombergs are just flawed. Seems like if it's not one thing, it's another. Now the front isn't leaking but the rear is blowing fuel from around the throttle bump rod. I had to limp it home by removing the fuel line from the rear carb and crimping it shut with tie wraps. Got it home and pulled the rear apart and looked everything over. Nothing really obvious wrong. Thinking they're just really touchy. Put it back together and back on. Seems to be fine now but really getting a bad feeling about using them at all. Those Carters are starting to sound really good. And damn, those Strombergs were NOT cheap. I'll test drive again tomorrow and see how things go. The carbs are level now though. I guess that's something.

[carbking]

It would have been nice if you had posted WHICH Stromberg carbs you are using.

 

However, Stromberg and Carter both made EXCELLENT carburetors, assuming one uses carburetors that match the application. If they are giving trouble, then either the application is wrong or the carbs need work.

 

As far as the drip at the throttle shaft, don't throw rocks at the carburetors, VOTE!

 

Fuel leak at throttle shaft AFTER engine is turned off

 

Jon

[Skidplate]

Oh no. I don't want to throw rocks at the carburetors. I want to throw the carburetors at the rocks. Thanks for the link. It was helpful but honestly I'm really getting the impression that Strombergs just may not be the quality they used to be. They might be pretty but they are the leakiest bas***ds I've ever seen. But I'll fight the battle a little longer but it's getting very old very fast. Sorry. I'm venting. But frustration is setting in. Thanks again for the input. It really IS appreciated. Oh, and they are 97's.

[Lawrence Helfand]

The Strombergs original to your car would be the way to go. 97's not so much. What you want is 2 AAV 16  7-42 series front carbs and a parallel linkage. Carter 509S is also suggested. Sorry but 97's should go to a Flathead ford 

[Lawrence Helfand]

[1937 Buick 66C]

Good evening,

 

I concur with 1939_Buick's post regarding the importance of keeping the carburetors level.  The entire design and flow of the carburetor, especially the graduated air correction and full throttle enrichment jet behavior depends on the fuel level in the bowl.  When the fuel level is not "balanced", the carburetor will not function as designed.  When I first purchased my 1937 Century, it had an intake manifold from a 1939 on it, tilting the carburetor causing all manner of strange behavior.  The engine would fuel starve under acceleration, then load up with excess fuel when braking.  I found and installed the correct intake manifold, and these problems vanished.  I note that this was also using a Carter WCD carburetor from a later Buick.

 

The Stromberg carburetors work very well, although the automatic choke mechanisms on the original AAV1 and AAV2 carburetors for 1937 and 1938 are unnecessarily complex and tedious to deal with.  Per my previous paragraph, the Carter WCD that was on my car when purchased worked more coherently and had a reliable automatic choke.  I retro-fitted to the correct Stromberg AA series carburetor when I restored the car (I do show it).  The Stromberg works find as a carburetor, although the automatic choke is a persistent challenge.

 

A small amount of fuel dripping from the throttle shafts after you have shut the engine off and it is hot is normal.  The carburetors get heat soaked from the exhaust manifold, the fuel in the bowl expands and leaks onto the throttle.  This dripping should stop after a few minutes.  The insulating blocks you have installed under the carburetors will reduce, but not eliminate this leakage.

[Skidplate]

I'll post pics when I get the heat shield made and installed. Got the carbs leveled. Still tweaking the linkage. Maybe just get used to moisture (gas) around the underside. It didn't really run bad when it was tilted just really dripped. How do you say "today was just a bad day at the races"?

[carbking]

17 hours ago, Skidplate said:

Oh no. I don't want to throw rocks at the carburetors. I want to throw the carburetors at the rocks. Thanks for the link. It was helpful but honestly I'm really getting the impression that Strombergs just may not be the quality they used to be. They might be pretty but they are the leakiest bas***ds I've ever seen. But I'll fight the battle a little longer but it's getting very old very fast. Sorry. I'm venting. But frustration is setting in. Thanks again for the input. It really IS appreciated. Oh, and they are 97's.

What???

 

Are you using the new production imitation Strombergs???

 

Either original Carters or original Strombergs would perform better. The new imitations are basically being built for the hot rod crowd.

 

Plus, they are smaller than the carbs used by Buick.

 

Jon

Edited February 28, 2023 by carbking (see edit history)

[Skidplate]

The thing is, every old carb I've ever had was an absolute nightmare to even remotely get to operate correctly. 80 years of who knows what's been done to it or what's been backfired through it is never a good thing. So yeah, here I am with new crap as apposed to old.  I've got a few more things to try but as it stands right now I'm really really not keen on throwing "good money after bad" as they say. I did get them leveled nicely and I'm working on a heat shield. " Patience Grasshopper". I just keep telling myself.

Edited February 28, 2023 by Skidplate (see edit history)

[carbking]

Thank you for the picture! It does help.

 

In the for what its worth category:

 

Those are two of the modern imitation 97's.

 

The 97's are 11 percent SMALLER than the correct Strombergs or Carters.

 

These have adjustable main metering jets.

 

The adjustable main metering jets are great on a SINGLE 1-barrel application.

 

For a carburetor/engine guru, they MIGHT be useful on a very worn engine with a SINGLE 2-barrel.

 

For a dual carb set-up, even a carburetor guru is going to require a multiple exhaust gas analyzer, with sensors on ALL exhaust ports to tune them correctly!!!!!

 

Suggestions:

 

(1) Acquire a pair of matched small original BUICK Stromberg AAV-16 carburetors

OR 

(1) Acquire a matched pair of small original BUICK Carter WCD carburetors

(2) Acquire a set of original BUICK Stromberg AAV-1 and AAV-16 carburetors and use progressive linkage (either (1) above would be better)

OR

(2) Acquire a set of original BUICK Carter WCD compound carburetion  carbs and use progressive linkage (either (1) above would be better)

(3??? -some number much lower than 3) Use what you have, and good luck.

 

Should you opt to use what you have, then the only other item I can provide would be a bottle of Bayer!  

 

EDIT: just took a better look at the full picture. Hand held tubing benders are relatively inexpensive. Tubing is relatively inexpensive. The use of hard fuel lines, is MUCH safer, and (opinion) looks much better than the flexible ones.

 

Jon

Edited February 28, 2023 by carbking (see edit history)

[Ben Bruce aka First Born]

Listen to Jon.

 

  Although I like MY WAY better.😁

 

  Ben

[Skidplate]

All great advice. I just put in an order for a case of Bayer. 🫤. So another piece of the puzzle, I'm at 5k-8k elevation (depending on where in the Rockies I'm driving) so the adjustable jets ARE (or at least might be) kinda useful. Also I do have O2 sensors on each of the two exhaust ports and a combined sensor further down the line. They do help a little but they certainly aren't the End All fix. The "two exhaust port" sensors feed a gauge under the hood and the "further down the line" sensor gauge is on my dash so I can get an Air/fuel feel while I'm driving. And they HAVE helped with tuning. Yeah, so for now I'll keep the carbs I have and continue taking drugs. I just finished cutting out the heat shield (.06 aluminum sheet") and should have that in place soon. I'll send pictures for your appropriate Laughing and Pointing. Cheers 

[Skidplate]

So I realized once I got them installed that they look a little stockcar-ie, but there you have it. Haven't started or drove it yet. The linkage is rubbing a little so I'll need to tweak a few things. But if the carbs stay cooler then progress was made. And now maybe when the fuel invariably drips, I won't freak out. Ok, I'll still freak out a little.

[Skidplate]

Ok, so when it was all said and done, and I do hope it's done, the list of things corrected to get it all right is as follows. Added the heat risers under the carbs and then corrected the carb tilt by machining the risers about 1-2 deg (guessing). Made the heat shield plates (aluminum) to not only reduce the heat coming off the exhaust but also to keep what fuel dripped from the carbs from landing on the exhaust. Replaced the existing mechanical fuel pump (never really surmised the fuel pressure it was actually putting out) with an electric pump (2-4psi) and mounted it at the output of the fuel tank on the crossmember just forward of the tank. Also added a 0-15 psi gauge (which was the lowest I could find) at my rear carb fuel line. It's not really very accurate since I'm only running 2-3 psi, but it's at least a reference. That  pump also specifically claims to not restrict fuel from flowing back to the tank after shutoff so will hopefully reduce the hot carb from dripping out the side on the exhaust and/or heat shield after shutoff. I kept having the rear carb blow fuel out of the plunger hole for no good reason (can you say Car Fire) but got it to quit after cleaning the float shutoff valve. Then it would come back after a few miles. I surmised that the float shutoff valve was in some way getting stuck open. The only thing I could figure was the really cool looking glass fuel filter that I had inline really didn't filter nearly what was necessary and was locking the tiny ass fuel shutoff valve open, so I installed a disposable filter above the glass filter (closer to the carb) to catch whatever was making the valve fail. I also adjusted the float down (bent the little tab while pushing down on the float) a little to get a little further away from that overflow threshold.  I haven't actually done more than a few laps around the block so I can't be sure that any of this has worked but I'm thinking really really positive. Oddly enough everything kinda sorta worked good before leveling the carbs (except for the leaking out the side issue of course). Leveling the carbs (which was necessary, I know) seemed to create "one step forward, five steps back". In the mean time, the high torque starter I ordered came in to replace the 6v grinder and I installed that. Say what you want but a modern starter rocks. Guess we'll see how everything else shakes out. Would really be nice to put some good clean miles on Balue by summer. But like they say, it's the final 10% of the build that's the hardest. Cheers

Edited March 23, 2023 by Skidplate (see edit history)

[bobj49f2]

I'm late to the discussion about the dual carb but thought I'd throw a couple of my set up just for kicks.  

 

After talking to Jon, the Carbking, I was able to find a matching Stomberg carb for the back.  I also bought kits from him to rebuild both carbs.  I have a '37 Special with a '40 engine and the dual carb set up from another '40-41 Buick.  My car is a Frankenstein car.  I used aluminum blocks to level the carbs.  Simple to do 1/2' thick aluminum bar, power miter box saw, a drill press and hole saw and a friend with a simple mill.

 

 

 

I also made brass block off plates for between the two manifolds. Bob's sells the brass block off plates for single but not for dual carbs.

 

 

I don't have the car on the road yet but I can start the engine and it seems to run great so far.