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1941 dual main Carters


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Peter, ball should be rolling free, when its low in the hole its in the start position Try this, with bearing in hole put the first piece(piston/metal, w/formed end) in the hole (long end at the bottom), then use a pencil or something to push firmly on the back of the piston, then turn the throttle valve, you should feel movement at the piston. If this works, problem is in the electrical part not the mechanical part of the switch.

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I know you're tired of hearing from me but here it goes...once again my initial diagnosis was bogus.  Tried the above and found both switches are good. Problem was/is in the short carb-to-carb linkage.  It wasn't allowing the front carb to fully engage. Back on track now and waiting for my hands to thaw before starting her up. Owning an old car is truly a humbling experience.  Thanks for hanging in with me. 

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2 hours ago, valk said:

Problem was/is in the short carb-to-carb linkage.  It wasn't allowing the front carb to fully engage.

 

Ahah!  I had a feeling that was the problem.

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So the short carb-to-carb rod has to be installed on the outside of the carb linkage mounting "arms" or else the rod and arm will hit on the front carb and limit the travel of the rod, preventing the starter from engaging.  I remounted the rod on the outside of the arm and everything works great.  I fired it up this morning and it started easily and ran great in my garage with the exception of the idle being too high. The front throttle stop screw is all the way out (the rear screw removed) so I have to lower the idle by some other method. Below are quotes by both Lawrence and Jon addressing this issue but I'm not totally clear of the method described. I know the idle can be lowered by adjusting the idle screws but I thought the best optimal setting of the screws was to maximize the idle speed.  Not so? 

I need to syn the chokes with a Uni-sync gizmo, alter my air cleaner and I'm essentially done. 

Peter

 

Hi Jon, I recently swapped my matching Strombergs on my 41 Century for matching 528S Carters and indeed they work better. My question is how does one achieve a lower idle if your already completely  backed out on the idle screw. My idle is still a touch to high and having read through the Carter adjustments in the workshop manual I am still clueless as to what path to take. Thanks Lawrence


If the throttle positioner screw (a.k.a. curb idle screw) is backed out so it is not touching, and the idle mixture control screws are turned in until thumb tight, the engine should stall. They are several "happy medium" combinations of the screws to acquire the desired idle.

 

J

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Make sure that the throttle blades are actually closing. It is possible to have the rods adjusted such that they don't allow the throttles to close even if you have the screws backed all the way out. This is how mine were at first. As Lawrence points out, you really need to make that pedal-to-front-carb rod as long as possible--I think I only have 3 or 4 threads in each end with a majority of the heim joint threads showing. That rod being a little too short would certainly prevent the throttles from closing all the way. Disconnect the throttle rod and see if it will idle properly. In fact, maybe do most of your tuning that way so that you know when you reconnect it if things get wonky, that's the problem.

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Good idea so I disconnected the long rod,  ran it and it was the same, too high.  Also made sure the other carb-to-carb rod was not the cause. My long rod is extended absolutely the most it can be, only 2 or 3 threads grabbing on each end and, being short, the pedal spring actually pulls the carb throttles tightly closed . 

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I think you need different linkage, but in the meantime, remove the linkage from one carb, loosen ALL of the nuts attaching both carbs to the intake, and with a helper, push both carbs toward each other and then tighten all of the nuts. There is a tiny bit of play in the carb throttle body to the studs. You might get enough slack to do some testing; but I would highly recommend redoing the linkage. Multiple carb linkage is very easy to fabricate. If you wish, give me a call during normal business hours, and I will explain. Then, if you wish, you can type it in this thread.

 

Jon

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5 hours ago, valk said:

Good idea so I disconnected the long rod,  ran it and it was the same, too high.  Also made sure the other carb-to-carb rod was not the cause. My long rod is extended absolutely the most it can be, only 2 or 3 threads grabbing on each end and, being short, the pedal spring actually pulls the carb throttles tightly closed . 

Hi Peter, The problem of the high idle on my setup turned out to be a gross imbalance of the carbs. I thought I had them very close as Matt had mentioned himself until he checked with the uniSync and it drove just great but when I got around to using my carb sync tool I found the front carb vacuum reading was way higher then the rear and when I balanced them out idle came way down and I had to screw the front idle adjuster in  a bit to get the idle where I wanted it. I was surprised it was that far off as I have been driving it for months with a slightly high idle which I actually liked. I think you will find this will fix it.   

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I ran it with the linkages disengaged and there was no change. But I let it fully warm up and the idle finally did go down on one of the carbs so I'm using that one to make throttle adjustments. I fiddled with the idle mix screws and ended up close to where I started at roughly 1 turn out. So I'm making progress, seems to run fine.  I'm going to let it cool down and try it again. I haven't uni-synced it yet but will when it arrives. I think it's all going to work out. I am very lucky and appreciative that I have my Buick buddies looking over my shoulder...

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Just a tip Peter. when using the uni sync you might find the red indicator go's right to the top on the carb with highest draw. You must open the airflow bypass in the center of the tool to get it within a working range. Until you balance the carbs further adjustments are premature. Also you will be making the balance adjustments with the carbs linked by rotating the rod until both readings match.

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Thanks Lawrence - good stuff. Matt mentioned making adjustments by twisting the rod but I wasn't sure until now what he was talking about. Sorry to apparently need advice at every turn...

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With respect to other's adjustment procedures, I prefer:

 

(1) disconnecting linkage from both carbs (leave it off completely).

(2) adjust idle mixture screws (all) at 1 turn (at this point, doesn't matter if too rich, only that they are the same).

(3) now use the Uni-Syn to balance the carbs.

(4) install the linkage on one carb, and fasten it in place.

(5) adjust the linkage such that it slips onto the second carb with no movement of either throttle arm (a tach should show no RPM variation).

(6) now ready to adjust mixture screws, and curb idle. Once the engine is turned off and cooled, the fast idle may be adjusted.

 

The reason I like to have the linkage totally removed is that I am CERTAIN that the rod isn't going to hang up somewhere and give me a false reading. I don't even like to think about adjusting the linkage on a 1958 Pontiac tripower at roughly 2 A.M. the day before one of the POCI conventions! ☹️

 

Jon.

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Awesome Jon. I'll do it just like that. One thing still hanging out there for me is whether or not the 2 idle screws on each carb need to be turned out the same amount. I always thought they should be but this hasn't been stated definitively.  

Peter

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Cranked her up this morning and she ran great.  My uni-syn doesn't arrive for a few days so I'm on hold for the moment.  I'll do the air cleaner in the meantime. 

Love this mod and wonder why Buick went through all the trouble of developing a more complicated progressive set up with 2 different carbs.  Gas milage can't be all that worse with 2 full carbs...I guess I'll find out. 

 

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I ran across this article from Team Buick. Has a lot of useful info on tuning, including a lot of info on the rear damper.  It also answers the question I had posed regarding the idle screws: 

"If either idle speed or idle mixture needs adjustment,.....turn each idle mixture screw the same amount in desired direction" 

https://www.teambuick.com/reference/carburetor_2x2.php

 

I'm trying to locate instructions for adjusting the choke, cold idle cam and de-loader, whatever they are... I thought CarbKing spelled it all out but I can't remember where!

Can anyone point me to instructions on how to adjust these? 

Thanks boys,

Peter

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Uni-syn arrived so I balanced the carbs today and took her for a spin. Drives great, no issues so I'm claiming victory and signing off. I intend to go through Jon's procedure above again just to be sure I got everything right but even now I am very happy with the results.  I made a crud collar/spacer out of rubber to fit over the carb throat to lift the air cleaner slightly so it would clear the rear carb but its a bit wobbly so I still have to resolve this but that's it other than fine tuning. Thanks so much for all the help - Tom, Lawrence, Matt, Jon and others. I wouldn't even had tried this without you guys having my back. 

Peter

buickduelcarb.jpg

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Yes, here's a heads up on what you are sacrificing by monkeying around with Buick's wonderful "Compound Carburetion" system (from the marketing folks, of course).  Apparently the 165 horse stock 320 with compound carburetion got lower gas mileage than the 107 horse 1940 single carb engine.  At least that's what they claim. 😉

 

fireball_news3.jpg.10b3269da9f696250f62431bcad9fae5.jpg

 

fireball_news5.jpg.461da473de82da9eb7816df0c1f39841.jpg

 

PS: Peter, your car looks great under the hood (as well as every place else).  As I've told you before, I find it difficult to look at photos of it!

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  1. My car seems to have settled at about 13.5 MPG on the highway, which isn't any worse than it was before. Not measurably better, but no worse. Performance is a little smoother and it might be more powerful, but it's hard to be sure on a car like this. I do think the dual carbs were wrongly blamed for crappy fuel economy during WWII--the cars just seem to get crappy fuel economy no matter what.
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Thanks Neil. My friends make fun of me for polishing my motorcycles more than I ride them. Turns out it's the same for the Buick.  38% power use at 80 MPH??  Those are some pretty lofty claims. I probably negated any MPG advantage by adding this second carb. I'm not overly concerned, though, since the car doesn't get driven frequently.  As Matt implied, these engines weren't built for economy. 

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After a few belts of my best bourbon, I took a soft head hammer to my air cleaner so it would clear the rear choke housing and seat properly on the rear main carb. Below are pics of the air cleaner after surgery, showing the factory dent on one end and my dent on the other, and I'm happy with the results.   It now seats as it should and since the new dent is under the air cleaner wing, it is out of sight and doesn't look funky or out of place, at least it looks ok to me. 

buickaircleaner.jpg

buickaircleaner1.jpg

buickaircleaner2.jpg

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Balancing both carb can be fun - sorta.    In my ‘other life’,   I used to ‘Aviate’ (“fly”  for those who know).   I built  several planes and two were powered with Rotax 912,  100 hp  German engines.    They were used by very many builders.    The engine had two side draft carb that needed careful balancing to produce smooth power.     The engine looked like the old VW  air cooled engines.   We used  two vacuum gages that were mounted side by side so you could set each side.    Not an easy way BUT,  I found a better way.    If you found a twin engine aircraft engine manifold gage,  you had the ability to tune the twin carb’s by watching the two needles as you got them jointed on top of each so it looked like one.    There are airplane parts salvage companies that you can check out and the prices vary but bargain.      I bought mine at a flee market for $30.00.    But than again, that was  about 10 years ago.     Aviation is not as busy as it used to be (thanks to gov. BS)  so the salvage business is not very business.   Thus, used parts from wrecked aircraft are not in demand.    This is a great way to balance our carb’s.  

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I'm very satisfied with the Uni-syn, does essentially the same thing just one carb at a time. I'll keep an eye out , though. 

 I feel a little badly about having to bash my air cleaner but the change is minimal and the alternative was to either install a spacer to lift the cleaner up out of the way (not a bad solution but it does raise the cleaner) or individual air cleaners for each carb (no way).  I'll touch up the scuffs and hope my Buick purist friends can forgive me....

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I have problems with my 1941 Buick Roadmaster’s front Carter carburetor.  A few days ago I started the car and the engine began racing uncontrollably and backfiring.  I removed the front carburetor for inspection.

 

The uncontrollable engine racing was caused by the metering rod shaft, which is part of the mechanism that lifts the metering rods, had jammed in the full throttle position.  After cleaning and careful inspection, the problem was that the carburetor’s top cover had slowly distorted over time, such that the two holes the metering rod shaft passes through, were no longer in the good alignment.  This misalignment produced excessive fiction for the free rotation of the shaft.

 

I also checked the part numbers on the metering rods and metering rod jets and discovered that the carburetor’s die-cast upper section was from a 1948-49 Buick Special Carter WCD 663 which was attached to the cast iron base from a 1941-42 compound carburetion large series engine (so the throttle linkage would match-up).  The correct 60, 70, & 90 Buick’s carburetor is a Carter 1-1/16 inch (this size is shown next to the venturies) WCD 490S (early) or WCD 533S.  The carburetor model can be confirmed by checking the metering rods and the metering rod jets.  The part numbers are stamped on the parts, as follows:

 

Std. metering rod: 75-473

Lean metering rod: 75-490

Metering rod jet: 120-121S

 

I am now rebuilding a Carter WCD 533S for my Roadmaster.

 

Img Rod.jpg

Img Carb Size.jpg

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Hi Grandpa, hope you're doing great.  Those  rod numbers coorespond to what Tom and I found as well. Was the mismatched carb the reason for the metering rod problem or are they unrelated? Good score on the 533S, there can't be too many of them left. I was truley fortunate to find mine. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Hi Valk.

The metering rod shaft problem, that I mentioned above, can occur on a WCD 533S carburetor, as the top cover (over the float bowls) is the same as the postwar Special carburetor.

 

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On a related subject -

I noticed variations in the manner that the wire cable for the starter switch is routed on restored cars.  The following pictures show what I believe is the correct cable routing.

Note that the factory photo does not show any insulation on the choke heater tubing.  The factory photo is of very earlier production and the insulation may have been added later.  The brass carburetor ID tag is normally bent down over the edge of the top cover of the carburetor.

Factory Photo.jpg

NOS_Carb.jpg

Install Carb 1.jpg

Install Carb 2.jpg

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Thanks Grandpa - that is how  I did it as well.  I am considering, however, routing the starting wire under the fuel/vacuum lines so they don't touch. You are one lucky fellow having that NOS Carter 533S. 

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Metering rods for 490S:

 

..and then there is this from the Mike's Carb which feels right:  stock rods for the 490 are 75-473. Optional rods for this carb are 75-490 (hi altitute), 75-491(even higher altitude), and 75-492 (hymalayas). As you noted, the 509 appears to use the very same rods so we may need another indicator to ID yours.

 

 

Carb # Jet Size Metering Rod Optional Metering Rod
486S .089 75-526 75-550, 75-551
487S .082 75-459 75-488, 75-489
490S .086 75-473 75-490, 75-491, 75-492
491S .0531    
509S .086 75-473 75-490, 75-491, 75-492
510S .0492    
549S .082 75-553 75-557, 75-558
551S .082 75-553 75-557, 75-558
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  • 2 weeks later...

Does anyone know what became of Buick experts "Jyrki" or "Alleycat"? These guys were around some time ago and apparently knew a tremendous amount about getting the most out of straight eights.  Wish they were still around.

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  • 6 months later...

Update: The larger main carbs (490s) from the 320 engine worked pretty well, actually, very well. My only complaint was that the car would occationally stumble slightly on take off. Mostly out of boredom, I purchased 2 528Ss, the main carb from the smaller engine that most folks use in this set up, and installed them yesterday. One  is a good rebuilt unit (thank you pont35cpe), the other NOS (thank you Lawrence). So far, it runs pretty much the same as the larger carbs but I haven't gone on a run yet.  One problem that has surfaced is that I'm having some issues balancing the carbs using a Uni-sync tool. Engine RPMs slow down and the engine will be close to stalling when I put the tool over the carb, even with the tool's air valve open so much the red indicator just goes to the first line. So I have to place the uni-sync on the carb, note the position of the red indicator, and quickly take it off before the RPMs slow down. Did anybody else have this issue when trying to syn the carbs? Chokes are wide open and all 4 idle mix screws 1 turn out. This wasn't a problem on the bigger carbs., I was able to place the tool on the carb and leave it there without the engine  slowing down. Any ideas?

Thanks,

Peter

uni-sync.jpg

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Went on a short spin with the new 528s and they performed well. No stumbling when cold and it ran just as smoothly as the larger carbs when warmed up. Plugs look good, just have to dial in the chokes as I have them wide open at the moment. It being so hot these days, they are really not needed. Looks like I’ll have 1 of the larger carbs up for sale if anyone is interested (490s/533s) I’m keeping 1 so it can go back to stock if desired. 
Case closed until the next project...

 

 

5BF939F8-C63E-4734-A172-8D97EBED3BC7.jpeg

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You can bump up the idle on the Uni-Syn for tuning purposes. Since both carbs will be locked together when you're done, turning the idle back down using the just the front carb's idle screw will control them both and they will stay balanced. Whether you're balancing them at 400 RPM or 900 RPM doesn't really make a difference. A higher idle will also give you a better reading somewhere in the middle of the gauge rather than down at the bottom.

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Thanks Matt. I’m a little puzzled that I need to advance the idle so much to keep the rpms up when using the tool. I guess the larger carbs sucked a lot more air.

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