1941 Buick Stromberg carb problems

Folks;

My '41 Roadmaster has the usual factory dual carb setup with Stromberg carbs front and back. The problem that keeps recurring is that it seems to draw raw fuel in down the venturis through the jets. I can see it dribbling in when I peer down with the air cleaner off and the car running. Both carbs have been rebuilt, and the front one only a month ago, and it was perfect when I put it on, but now I have the same issue once again. I have another, identical front (AAV 16) carb, rebuilt many years ago, and it runs even worse with that one. It gets a bit expensive to have it done time and again, and once done, I think that it should be good for a number of years. I think that there must be a small passage or something that clogs up.

A bit other info, the engine is rebuilt, and has good compression, the car gets driven 2-3 times a week during the good weather, there is a filter in the line near the tank, I use fuel stabilizer in the off season. I've disassembled the carb and it all looks good, nice and clean, like one would expect, but it just doesn't run right.

Float level is correct, as verified by checking the sight plug in the side of the carb. Back one too is set correctly. Currently running an electric fuel pump, and have bypassed the stock mechanical one.

Idle is not bad, but the when cruising, it has what I used to call "chuggle", that means it feels like it is surging, and letting back, repeatedly. Under mild to heavy load, it drives well, but at cruise and light de-excell throttle, it acts up.

Under full power it pulls strong in all gears as fast I dare go.

The distributor has been serviced and seems to be working well, including the vaccumn advance.

I'm an experienced "backyard" mechanic and have worked on old Buicks for many years.

So, anyone been through this with these carbs, and can help me? What am I missing?

Keith

How much fuel pressure do you have from the electric fuel pump? excess pressure will override the float and needle valve. Match the pressure to the specs from the original mechanical pump.

Bob Engle

The pump is set for 6 psi and is mounted near the tank. But I don't think that's the problem, as it the same way with the mechanical pump.

Keith

Your electric pump may (or may not) be the issue.

Consider a major difference between an electric pump and a mechanical pump:

The electric pump output is independent of the engine RPM. It delivers the same pressure and volume at all times.

The mechanical pump, driven off of the camshaft, will change volume (sometimes pressure) as the RPM of the engine changes.

For a test only, set the fuel level in the carburetor 1/16th of an inch high (again, this is for testing only). Go drive the car at your cruise speed, and see if the surging changes. If the surging is reduced, you might wish to try (A) a higher volume electric pump, ( a mechanical pump, or © increase the diameter of the main metering jets my 0.001 inch.

Do not leave the fuel level high, as you could have unwanted bleedover if the car is parked on an incline.

And just for the record, the suggested pressure at the carb by Stromberg was 5 psi. Your 6 psi at the pump located at the tank should not be an issue.

Jon.

Interesting test, I'll give it a try.

Also, I perhaps was not clear in my original post, but this is an issue that I've had for a number of years, off and on, but the electric pump is a very recent addition. Like a few weeks ago, for hopefully(!) better reliability, as this car is a driver, and I drive as often as I can. After the last carb rebuild, I was having some high speed missing, and considered that the mechanical pump could beto blame, so after the installation of the electric, that issue is cured. But the surging hasn't changed. As I said before, now at full throttle it will rev past my courage limit in all gears.

Thank you for your responses.

Keith

With dual carbs, is it possible that the idle butterfly settings are incorrect? This might cause one carb to pull most of the air thru it and induce fueling while the other is contributing very little. (If the idle mixture setting is too lean and the butterfly is opened too far to compensate.) Add that scenario to the other carb having the butterfly tightly closed.

I am assuming that your primary carb is the one dribbling. Have you synchronized both carbs?

Your last post would seem to eliminate the electric pump as the culprit.

Ethanol based fuel has less energy than gasoline. It may be this is the cause of your surging. Raising the fuel level slightly will reduce the amount of negative pressure in the main metering circuit necessary to effect bleedover (thus causing slightly more fuel to flow through main metering).

When you are running under wide open throttle, the power jet augments the main metering jet.

Are you running the original dual two-barrel setup with front/primary and rear/secondary; or have you converted to two primary running all the time?

Jon.

To answer both queries, I have got the carbs both synchronized. Yes I did have that issue, where one was pulling more air than the other, which was giving me poor idle, which smoothed out once they were in syn.

Also, I am running the stock front primary/rear secondary. It is the front carb that is dribbling. Is there an advantage to running two primaries? I do have a spare front carb.

Keith

I read a tip recently, in one of the car club magazines, that said the ethanol in the fuel causes carburetor gaskets to shrink. This could cause leakage of excess fuel from the carburetor bowl--in my 1950 Roadmaster it causes vacuum leaks in the carburetor. The magazine tip said to add one cup of diesel fuel to each full tank of gasoline. This keeps the gaskets moist and lubricated, and counteracts the effect of the ethanol, which draws moisture out of everything it touches. I have not tried it yet, but it sounds right, and I intend to try it.

Pete Phillips, BCA #7338

Leonard, Texas

Keith - I would suggest getting your current issue corrected before doing the conversion. Don't add an additional variable into the mix.

Once you have things running as they were designed; you might wish to try two fronts. Having both carbs working all of the time improves the fuel distribution to the rear cylinders, and the engine will run more smoothly.

Pete - different carb companies used different gasket material. Stromberg did use a material that would shrink, but discontinued use about 1933 or so. The later Stromberg gaskets did not shrink. Zenith the same way. Carter used a material for their thin gaskets in the 1930's, '40's, and 50's that would shrink. This material was discontinued by Carter about 1957. Rochester used a similiar material from 1949 through the mid 1960's. This material would dry out even in the sealed repair kits, and new old stock gaskets would be shrunk.

The shrinkable gaskets would shrink from having no fuel in the carburetor (sitting long periods without being started). In the presence of fuel, no problems. I am not going to argue with the article you read, as I don't know; however, I have not personally seen issues with carburetors on vehicles that were driven, and have on those that are not.

EDIT: After posting the above, did a little research. Carter, Stromberg, and Zenith all in the 1920's and 1930's suggested soaking some of their gaskets in denatured alcohol prior to use. This would lead me to believe the ethanol would not cause gasket shrinkage.

Jon

So just a question as I have little experience with multi-carbs. If you set both as primary, does that mean changing the linkage so that both open in parallel as opposed to serially? And does that also mean changing the secondary carb to a primary type with the choke? I would suspect that average gas mileage would suffer a bit - does it?

Cheers, Dave

Dave - if you use two primary carbs, then both operate simultaneously. Different ideas exist on whether to use choke on both or just one. Personally, I use choke on both, as the choke butterfly improves lower RPM air velocity (it acts as a straightening vane for the incoming air).

As to fuel economy:

It may (or may not) be necessary to change the jetting slightly using this configuration. However, every single multiple carb set-up that we have done this way IMPROVES fuel economy (although sometimes marginally). Of course, fuel economy certainly could suffer, depending on the "shoe size" of the driver!

The only times we will use progressive linkage on multiple carbureted engines is on numbers matching show cars with original multiple carb set-ups. This is true for V-8's with dual 4-barrels as well.

Jon.

Well Folks, I finally got some time to get to try "carbking's" suggestion, raising the float level a bit, and it seemed to run worse, then I lowered a bit, and it ran a bit better, but still not right.

Also, to make sure that the new electric pump was not putting out too much pressure, I checked it, and supplied a max of 4 1/2 lbs at the carb. inlet, which is correct for this car. The carb itself looks really nice and clean inside and out, as one would expect from a recent rebuild. Idle quality is decent, except with the higher float setting, and then it seemed to be running too rich at idle, which I think would make sense.

I have another Stromberg AAV 16 (front) that I might try on it. Its' supposed to be an older rebuild, but otherwise I don't know its' pedigree.

On Sat I have to fix the brakes and tie rod ends on my daughter's car, so hopefully I can get get back to the '41 after that. Next weekend I have a long tour I really want to do with my '41, so I hope that I can get it running well by then.

Keith

Well, I tried the other carb (same type, an AAV-16) and it runs worse overall, though the "surging" does seem to be not quite as bad.

I blew out the passages I could get at by taking the top off (I don't want to take it all apart right now) on the rebuild, and all seems to be clear, so I reinstalled it and its' running about the same. Reading though the manuals it seems like either the main metering system is at fault somehow, or the power circuit is putting fuel in when it shouldn't. There is a piston that is held up by vacumn, and a little valve underneath that operate the power circuit, could the issue be related to wear in the bore, or that valve leaking?

Needless to say, I am getting very fustrated with this.

Keith

You have in each post listed the carburetor type (AAV-16) but never the identification number.

Stromberg made dozens of different type AAV-16 carbs.

If you look straight down on the airhorn (top casting) of the AAV-16 along one of the ends you should see a stamped (recessed, not raised) code number. The code for Buick is 7; so the number should be 7-???. This number will positively identify the application of the carburetor.

Jon.

Yes, the carb in question is stamped 7-39.

Keith

OK. correct front carb for 1941 320 engine.

Jon.

That's good to know, as it was on the car when I bought it, but one never knows. But what do you think is wrong with it?

Keith

Mine was a 248 ci straight eight (small engine) but all factory . I went threw 4 or more of these set ups over the years and making sure the heat riser butterflies move freely also the rear carb aluminum riser butterfly is a wieghted pendulum . This wieghted pendulum blocks all suction unltil the accelerator pedal moves the throttle butterflies then the riser butterflies open . If these wieghted butterflies are open at idle or while just tootiling around town it is too much gas . I have made a youtube video of my factory 248 straight running , maybe you are missing the aluminum wieghted butterfly spacer ?

Buickkuhn;

I do have the aluminum spacer with the weighted spacer, though it was seized solid when I got the car. I have checked that from time to time to make sure that it is still working, and it seems to be.

The heat risers are seized, and I went through a lot of work to get freed, heat, soaking in various solvent oils, to no avail. They are however, in the open position.

Keith

Hopefully I will be getting back into this problem in a day or so, so anyone with anything else to add?

Keith

I put a small fuel pressure gauge and a Holley adjustable flow regulator use tee fittings right b4 the carb so I could see what pressure the carb was getting from the 6volt elec. pump.It allowed me to dial the idle pressure in right under the hood. When I power up the pump I can watch the pressure increase and hit the key for a quick start. Especially nice after sitting for awhile. Saves strain on starter and battery. Pump is obviously not positive displacement as it seems to just happily cavitate without overheating or other problems as it comes up to regulated pressure. I have no return line back to tank. Pump was under 50 bucks from Auto zone has not failed and seems to have adequate flow for accel/high speed cruise. This is on my 40 super 248. My 41 320 cent has dual Rochester 2 barrel gc's that are a 4 bolt pattern with 3 to 4 bolt carb adapters available from Speedway motors. Running both not progressive. It's a work in progress as it' s only yard driving currently as brakes and fuel tank need restore. Putting riser tubes on Rochester's to clear carb choke body interference & hopefully use dual carb air clnr top with K&N filter bottom in place of oilbath stocker.

Hopefully I will be getting back into this problem in a day or so, so anyone with anything else to add?

Keith

My '41 (along with the '56) is away for the winter at a friend place so that my wife's neglected '68 Wildcat convert can get time in the nice heated garage.

So, not too much will be going on with the '41 for a few months, however I just bought a pair of Carter's off of the 'bay, and will rebuild them in the new year, so I'm very interested in seeing if this is an improvement in drivability when I get it out in the Spring.

Keith

So what ever happened to the surging?......I am dying to know....same issue on a  51 special w/263 single 2 barrel stromberg... I was leaning toward an emulsion tube blockage..... 

Interesting reading. My 41 Century 2 door 66s has Strombergs and my four door 41 Century has Carters. The Carter motor is very smooth right from cold while the Stromberg motor needs to warm up quite a bit to be as smooth right from startup. Does anyone have a definitive evaluation of how they compare? Certainly one should prevail over the other in function? 

18 hours ago, darcus said:

So what ever happened to the surging?......I am dying to know....same issue on a  51 special w/263 single 2 barrel stromberg... I was leaning toward an emulsion tube blockage..... 

Yes! I'm very interested in hearing more about this too. My 41 with a 51 263 and two stromberg 97s also surges or "chuggles" at low to mid range sustained throttle position.

If both are professionally rebuilt and the engine is reasonably stock, the results should be equal. The Carter are easier to modify for a modified engine because of the metering rod technology.

Jon.

This is a really interesting topic.   I need someone to help my memory in regard to these carburetors used in the Buick "Compound  Carburetion" system.  Somewhere I read that the carburetors used here were not the same as used on the single carburetor engines of the 1940 models and that using carburetors designed for the single carb system would not function properly in the dual carb setup.   I think the reason was that they looked similar but the internals were sized differently.

Joe, BCA 33493

Engines are air pumps (with fuel and spark added).

An air pump will pump a certain amount of air, depending on, among other things: RPM, displacement, and the efficiency of the pump.

A carburetor will flow a certain amount of air. Two carburetors of exactly the same size will NOT flow exactly twice the amount of air as one when both are installed together on one engine.

So, when dual carbs are used on basically the same engine, FOR BEST RESULTS, each carb should be somewhat smaller than a single carb.

From memory (not always a good idea), the 1940 Buick single carb on the large engine had a main venturi size of 1 3/16 inch, and the dual carbs of 1941 for the same engine had a main venturi size of 1 1/16 inch.

Thus, each of the two 1941 carbs was approximately 20 percent smaller.

When one considers the factor mentioned in paragraph three above, the two smaller carbs of 1941 PROBABLY (without having data from a flow bench) would flow a total of 20~25 percent more total air than the 1940 single carburetor.

Jon.

Thanks for your post above carbking.  These dual carburetors must be quite rare if they were used only in 1941-42, unless there were other vehicles that used the same size carburetor.  If someone attempted to use two carburetors from the 1940 cars, then these would be much too large.  Is this correct?

Joe, BCA 33493

Joseph, carbking knows way more than I, perhaps he'll add his opinion, but on an engine with a stock cam, I think that the answer is yes. If you are using a higher lift cam, then your engine will likely be able to use the increased flow. Some people have set them up to run with two fronts, instead of the factory front and rear, and like the way it works, and on the big engine, they've used carbs from the smaller engine. Don't know what they do to set the small engine like that.

 My car is running much better now that I am using Carters in place of the Strombergs.

 Keith

Glad to hear it is running better.  I always liked the Carter carburetors over the Strombergs but it just might be I have had good luck with them.

My uncle used to be a parts and then a service manager in Buick, Olds and Cadillac dealerships in Westchester County, NY.  He remembered the dual carb setup that he always called "compound carburetion" and the problems they had with them.  One problem was that the carburetors had to be synchronized by way of adjusting I believe the linkage rod so that the secondary came into play at the right time.  Then there was the problem of gasoline availability during and right after the war and how some owners would request that they block off one carb opening and run with just the main to save gasoline or use manifolds from a 1940 or earlier model to run one carburetor.

Joe, BCA 33493

6 hours ago, Joseph P. Indusi said:

Thanks for your post above carbking.  These dual carburetors must be quite rare if they were used only in 1941-42, unless there were other vehicles that used the same size carburetor.  If someone attempted to use two carburetors from the 1940 cars, then these would be much too large.  Is this correct?

Joe, BCA 33493

Joe - yes, this is true, HOWEVER:

For those less interested in "numbers matching", or in this case original carburetors, we have had excellent success on the large engine by using two single carburetors from the small engine AND RUNNING BOTH SIMULTANEOUSLY!

Also, once we set up a set of non-Buick carbs on the small engine, again running both carbs simultaneously.

Running the carbs simultaneously REALLY helps the A/F ratio average for all cylinders, and results in much smoother performance, not to mention improved power AND economy. Really not that difficult to synchronize the two carbs running simultaneously, but synchronization should be done.

Just to add a bit more information, Buick was working with Stromberg on compound carburetion as early as 1935! I have information in the Stromberg factory records that indicate Stromberg built some experimental SINGLE BARREL carburetors to be used in tandem for Buick in 1935. Of course, these never reached production. Obviously, the engineers were trying to get better cylinder fill ratios by spreading out the carburetors even then.

And Keith, glad you are happy with your Carters; but there is something with your Strombergs not right. As I posted earlier, there should be no difference on a basically stock engine. Although it sounds like you have learned the ABC's of carburetion! (A)lways (B)uy (C)arter  

Jon.

1 hour ago, carbking said:

And Keith, glad you are happy with your Carters; but there is something with your Strombergs not right. As I posted earlier, there should be no difference on a basically stock engine. Although it sounds like you have learned the ABC's of carburetion! (A)lways (B)uy (C)arter  

Thanks, I'll remember that!

Keith

Carbking:

Thanks for the education and history.  Great post and thanks for sharing your knowledge.

Joe

I was basically sick of spending money on the Stombergs and not getting the results I wanted, which was simply to have the engine run as it was designed to. Being in Canada, sending this stuff to the US costs lots more, and then if I wondered, What if hundreds more and hey still don't work right?". So I opted to find Carters and replace the Berg's.

Keith

I had the surging problem on my 38 and also could see gas dribling sometimes with the air cleaner off. I tried a rebuilt carb with the same results. I also have an electric fuel pump in the line along with the mechanical but I do not use the electric one, only if it sits for a week or so then it is used to prime the carb before I start it. Just for the heck of it I added a pressure regulator I got from Summitt and its never had another problem, runs perfect!

Interesting, Dave. What pressure do you have it set for?

Keith

I actually like the Strombergs and have had good luck tuning the pair on my Limited. The sucker runs like a freight train and the transition between one carb and two is seamless. The idle isn't quite as smooth as I'd like, but I'm not sure I can blame the carburetors for that. I'm reluctant to change much on them simply because it runs so well.

That said, I'm going to have to tear it all off and do something about the exhaust manifolds. I'm planning on building some stainless headers to replace the cast iron--I've had enough there and it can only be a good thing to de-couple the exhaust and intake manifolds and get some heat out of the carbs. Because of that alone, I'm sure the carburetors will need some fresh tuning once the thing is back together. I'm kind of toying with the idea of going with a pair of primary carbs from a small series and putting them in parallel with a simple linkage rather than in series like the factory. Heck, I already have a pair of Rochesters that will bolt on, although they're ancient and need rebuilding. Carbking has suggested that it improves driveability, power, and economy. I don't want to go too far outside of stock, but since this will be our primary tour car, some reliability and some added oomph sure wouldn't hurt. I haven't decided specifically what I'll do, but I do have some slight upgrades in mind to make this Limited the ultimate tour car. As long as I'm keeping it, why not use it as often as possible?

1 hour ago, Buicknutty said:

Interesting, Dave. What pressure do you have it set for?

Keith

Kieth the one i got was a 12-803 from SUMMITT. I turned the screw about one full turn in the direction it says to lesson the pressure, I have no idea what the pressure actually is.