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MG MGB Technical - 32/36 DGV carburetor conversion

Hello,

I am considering swaping my twin SUs with a 32/36 DGV carburetor from MGS Northwest ($399).

http://www.northwestimportparts.com

Moss motors also has one for $499.

There is a lot of web sites out there to walk me through the process, but I am not sure if I have to change the exaust manifold or not.

My 79 MGB has twin carbs and I heard that you only had to swap out the exaust manifold if you are replacing a single carb setup. Anyone know if this is true?

If I do have to replace the exaust manifold, do I just replace the manifold itself or do I have to replace the pipes...

Is there anything else I need to know before starting this project...

The weather is gonna get nice soon...
TCC Todd Canfield

Todd,

If your car is a 79, then you are already starting with a modified version of the MGB because the 79 would have come equiped with the catalytic converter and single zinith-stromberg as original equipment. If the intake manifold used by the Weber fits in the slots vacated by your SU set-up, then there would be no need to replace the exhaust manifold. You may have to shim at the places where the intake and exhaust abutt. The only time it is necessary to change both manifolds is when you are converting from the combination intake-exhaust system of the rubber bumper cars.

Doug
D. Cook

Thank you Doug, I had a feeling that the twin carb setup was not factory...

I am not sure I understand what you mean by 'shim at the places where the intake and exhaust abutt'. Do you mean if they are touching, put a chim between them or are you saying to grind down the manifold to make for more clearance?

One of the weber downdraft kits I was looking at, comes with a pekok header...kind of spendy though at $615.

http://www.brittek.com/index.html

Happy motoring!
TCC Todd Canfield

Why would you replace twin SU's with a downdraft Weber? The twin SU's are a MUCH better carb setup IMHO, and have the advantage of costing you...nothing, since a previous owner has done it for you. Not sure what exhaust you have, if it is an early-style manifold with double downpipes, keep that on the car, as it is hard to improve on.

Paul K

The $615 kit you are looking at is not a Weber 32/36, it's a 38/38 DGES Weber and Peco header which explains the cost. Clifton
Clifton Gordon

Todd: You do not need a header system. The exhaust manifold and system you already have with the twin SU's will work with the Weber and actually have some advantages over any header.
If you buy a new Weber you can get the correct one for the exhaust you have and not need to shim it. You will have to measure the exhaust manifold flange thickness. The folks who sell you the Weber can advise on the best way to do this.
The Weber comes with a manual, water, or electric choke for various prices. I like the electric for simplicity. I recommend Brit-Tek as a parts supplier and Bob Ford is very easy to deal with. He can tell you which intake manifold Weber will work with your present system.

Now I have to ask you why do you want to replace the SU's? You will get neither a performance advantage nor a performance loss with the Weber over the SU's. If your SU's are worn out you can get them rebuilt by Joe Curto or by John Twist at University Motors for about the same or less than the Weber set up. I recommend this route because SU's are original on MG (though not on your '79) and because I prefer their slightly sharper throttle response.

One last suggestion is to contact Victoria British who have a Winter sale on now that may have new HS4 SU's for the same or less than a rebuild or the Weber. the catch is you need to be sure yours are HS and not HIF as these are much more expensive.

Good luck with whatever you choose and keep us posted.
Terry

Todd-
Paul K. is correct in telling you to stay with the dual SUs. The Weber downdraft 32/36 DGV is primarily an econo-carburetor. It also makes the engine look as though it was pirated from a Russian tractor. Its usually included adapter manifold has the flow characteristics of a bathtub with a hole in each side. This is due to Pierce Manifolds, its distributor, bundling their own poorly designed intake manifold with the carburetor and selling the resulting package as a kit. Just as the fuel suspended in the incoming fuel/air charge is denser and heavier than the air, its inertia thus causing it to go towards the outside of the curved intake manifold, biasing the fuel towards the intake valves of #1 and #4 cylinders and thus creating a richer mixture for those cylinders, the intake manifold shape for the downdraft Weber DGV carburetors is actually rather poor. As a result, virtually every example of this combination that I've encountered or ever heard of had a "flat spot" in the powerband from 1,500 to 2,500 RPM where throttle response was poor. This "flat spot" can be eliminated by using a Cannon intake manifold instead. However, this will not eliminate the problems imposed by the restrictive airfilter that Pierce Manifolds supplies with it in its kit. The Weber 32/36 is a progressive type carburetor. This means that the 32mm primary bore is opening with the throttle first, but the 36mm secondary bore does not open until the accelerator pedal is about 2/3rds of the way to the floor. Since 1 1/2" equals about 38mm (1.496"), there are two considerations. First, the two bores of a Weber DGV 32/36 series carburetor together can not possibly flow as much air/fuel as twin 1 1/2" SU carburetors at full throttle due to the smaller bores of the Weber design. Second, the progressive opening of the 32mm and the 36mm bores of the Weber design do not flow as efficiently as the simultaneous flow of the 1 1/2? SUs when at less than full throttle. It is simply impossible for a Weber DGV 32/36 to perform as well as twin SU HS4 or HIF4 carburetors. If your goal is performance, remember that the Weber DGV 32/36 is vastly inferior to the twin SUs. Its cousin, the Weber downdraft DGES 38/38, mounts on the same intake manifold and gives more torque at low engine speeds, but can make the engine difficult to start in cool weather and has developed a reputation for troublesome running at low and moderate engine speeds.
Steve S.

WOW! Thank you all for your responses. I appreciate you taking the time to educate me on the issues...

I am not 100% decided that I want to go to a weber downdraft (either 32/36 or 38/38), but am facing a few problems with the existing setup (Why do I want to replace the twin SUs?).

1)One of the carbs (pistons?..the big thing moving up and down) sticks when the car is first started. It takes me 5 minutes to get it warmed up. After that it works fine. I have posted this problem and talked to the local MG guy, but have not have found a solution. I am sure if they worked, I would not be in such a hurry to replace the twin setup.

2)The twin setup does not have air cleaners. I am told there are K&N filters that may work, but (since I am new to this adventure), I dont know what type of Twin Carbs I have (HS4 or HIF4). Also, someone has tried to put air filters on the twin setup and re-threaded the air cleaner bolt holes. They may have been stripped. I am afraid any K&N filter I get will not fit. I dont like 'unclean' air getting in my motor...

BTW, what does HS and HIF mean and how do I know what type I have?

Thanks again to all that posted (especially Steve..you gave me much to think about)

Todd
TCC Todd Canfield

Todd,

Try this link http://www.mossmotors.com/Browse/PlateMenuProducts.aspx?WebCatalogID=8&PlateTypeID=1&SubcomponentID=79 and see which carbs, HS or HIF most closely resemble your carbs. The easiest point of indentification for me is that the HS4's have separate float bowls to the outside (looking at the carbs from the left front fender) of the carbs themselves.

I would recommend sending your carbs to Joe Curto for rebuilding. That should cure your sticking problem. http://www.joecurtoinc.com

You do need to get some filters on the carbs, unless you like rebuilding engines. The filter bolts do not thread into the carb bodies themselves, but into U-brackets with integral nuts that fit behind the flanges. The K & N kit with the aluminum plate is very nice, but a bit pricey. I have them on my GT, and they look and work very well. If you don't have the stock backplates (radiused fittings to smooth the airflow) you'll need to pick up a pair. Should be some used ones out there going very cheap.


Paul K

Todd,

The HS style carbs (Horizontal Side float) have the fuel float bowls located to the side of the carburetor body. The fuel mixture is adjusted via a nut underneath directly setting the height of the jet tube. The HIF (Horizontal Integral Float) has the fuel float bowls incorporated in the lower portion of the carb body. The fuel mixture is adjusted via an adjustment screw from the side of the carb body. They also incorporate a temperature compensating mechanism for the mixture.
HTH
Tom
Tom Sotomayor

I think the HIF carbs are supposed to have threaded holes for the filters. I have two sets of HIF's and both have threaded filter holes, 5/16" coarse threads. They do not have helicoils. Moss lists the HF filter bolt as a fine thread #322-150, for the HIF they show #322-175, coarse thread. I don't think there is enough room around HIF carb bowls to install u brackets used on HS carbs. Regards, Clifton
Clifton Gordon

Thanks Clifton, for the clarification. I don't have any cars HIF-equipped, I just assumed they were the same as HS. You learn something new every day here.

Paul K

Todd. I am currently running the Weber DGV, the manual choke model, on both my daughter's 77B and my own 79 B. I wish we could run the dual SUs, but, due to emissions inspection requirements, we cannot. I use the TWM intake manifolds which have a chamber below the carb for a water heater. Riverside, I believe, offers a similar modification for the Pierce intake manifolds. With this, you run a hose from the rear of the head, the original take off point for the water choke on the Z-S to the intake manifold, then to the lower radiator hose. A much better set-up than the Pierce manifold and hard to find. (I have purchased all that I could find locally--all on the used part market.) The Weber DGV is fully capable of meeting all of Arizona's stringent emissions requirements and does so in fine fashion. But.

The twin SU carbs are the way to go for both best performance and best economy. My 68 GT, with its twin SUs gets as good fuel economy as my 79 with its Weber. Neither carb is any problem to set up and maintain once you understand them. Paul Hunt's website has some excellent information on how to set them up. I have dealt with both Joe Curto and John Twist over the years and do not have any preference. Both are capable of providing excellent service. Were it I, I would either purchase a new set of HS-4 carbs and install them, or I would have my present carbs rebuilt by Joe or John. Les
Les Bengtson

Todd, you have inadvertently opened a can of worms here (again)with the SU vs. Weber DGV.
The DGV is in no way an economy carb. It is used on Formula Ford racing engines (1.6 and 2.0) and also on 2 litre sports racers (smaller versions of LeMans type cars).
The B series engine actually shows 1 or 2 HP more than SU's on the rolling road dynomometer with a properly jetted ,well set up Weber. The progressive linkage design works quite well performance wise, keeping mixture velocities high at lower RPM's until the transition to the second barrel at higher revs with more throttle. The SU's do the same thing with their tapered needle design. At cruising speeds the progressive linkage also delivers good fuel mileage. And performance is available via your right foot. After all, don't you floor the throttle pedal when you want maximum acceleration? As far as the manifold design I have found that it is cylinders 2 and 3 that tend to run rich rather than 1 and 4 and this is cured with very careful mixture adjustment. The carb comes with a K&N filter assembly of admittedly narrow configuration. I use a Longflo oval filter that offers a good deal more element exposure for increased flow.

My personal experience with both carb setups in the same car is that there is no noticeable difference in acceleration times but the SU's do feel stronger at lower rev ranges while the Weber comes on strong over 3000 RPM. You do have to keep in mind that while the Weber is decent right out of the box, careful mixture setting is VERY important to avoiding the flat spot a lot of people experience on full throttle at lower revs. If you have other performance upgrades like a flowed head or stronger camshaft you will need to rejet the Weber for best power.

In short, there is NO LOSS in performance with a properly set up Weber DGV when compared with dual 1.5 SU's. I still prefer SU's for originality and low rev throttle response. For high performance engines the SU's have the additional advantage of an easy cold air box addition. I run SU's on my '73 GT and a Weber on my '77 B. I have no hesitation recommending a Weber as a good cost effective replacement for the single Zenith on post 74 MGB's.
Terry

I have installed a Weber DVg on my 64 B , which has had head work, hotter cam and some other things done to it. As I have done all these things myself I can only guess what stage of tune it is in, #2 probably. It was built for reliability and ease of driving. I have rejetted the carb and spent lots of time adjusting it so it runs pretty well. It may not have the responce that SU's have but the 4 or 5 other B's in the area ( some with much work done ) have trouble staying with me on the hills around here. I can pull most hills in 5th or 4th if I have to slow down for a cow in the road and I don't have to tune the carb regulary. Maintenance is necessary to our auto's, and the less time that I spend on it the more time I have to drive. Everyone to there own. Happiness is is the day that I wake my car up from her winter nap and that day is tomorrow.
E kulick

I am not an amature around the engine. I have been working on cars my whole life, but when I read some of your posts, I realize how much I DONT know. :-/

I appreciate all your input. I think I am coming to realize that my 'B...is what it is' and the decisions we make (SU vs. Weber DGV for example) regarding our cars are going to be unique for the owner (and car of course...given the existing configuration and condition...).

Regarding my Carb problems...I think I will email a picture of my twin SUs to one of the companies mentioned above and see if the threaded air cleaner bolt holes (only on one side of the carb) are going to be a problem (for a rebuild).

Depending on that answer, I may rebuild my existing setup or buy new HS-4s.

Thanks to All

Todd
79 MG-B-eautiful
TCC Todd Canfield


For what it's worth I have the 32/36 DGV Weber on my '67 BGT and I must say that it performs wonderfully. I still have the SUs which I will probably rebuild eventually but until the Weber is on its last legs, it's staying on my car. While I always try to shoot for originality, I also have to accomodate for driveability, and the Weber seems to fit the bill.

Rgds,
Aaron Greenberg
owner- MB Classic, LLC
Service and Restoration of Vintage Mercedes-Benz Automobiles
'67 BGT
'76 TR6

Aaron

All,

If I understood Pauls email above, I believe I have the HS-4 type Carb. Here is a picture...

http://www.geocities.com/vbprogrammertodd/Image001.jpg

HS-4...right?

If you look at the picture, you can see the holes on the left carb are threaded and the holes on the right are not...making mounting an airclear, perhaps, a little difficult.

If these are HS-4s then they must have been off a pre 1973 MGB. (72 being the last year).

Comments? Thanks

Todd C
TCC Todd Canfield

Sorry, the GD link doesn't work...

Here are the pictures of my carb...

http://home.comcast.net/~tcanfield/index.html

or this

http://www.geocities.com/vbprogrammertodd


TCC Todd Canfield

Todd,
Yep, those are HS4's. The tapped holes shouldn't be an issue. The factory used "U" shaped plates with tapped bosses (nuts) on them as Paul mentioned. Even if the holes are now a little too big the stock attachment should work fine.

After looking at your pictures there are a couple of things you'll want to take care of. Fit some overflow tubes to the float bowls! They will attach to the short rubber hoses coming off of the float bowl lids. Put one each on the front and back carbs. Copper refridgeration tubing works fine for this and is available from a hardware store. Not much fun having a carb overflow onto a hot exhaust manifold - POOF!

It also looks like you may not have a vacuum check valve on the large vacuum hose going from the manifold to the brake booster (although sometimes they did mount one to the booster itself). The angled takeoff on the rear corner of the intake manifold will accept the stock check valve with no mods, or you can adapt one to fit in your existing hose.

Good luck,
Tom
Tom Sotomayor

Todd. Tom is correct that you have HS series carbs. In addition to what he has mentioned, the set up of your choke system is suspect. It has been rigged up by someone rather than being one of the two factory pattern set ups. Take a look at the Moss catalog or Clausager's Original MGB to see how the factory did it. I suspect that this conversion was done in a somewhat erratic manner and starting over, rebuilding and making things correct as needed, will result in a lot better performance. Les
Les Bengtson

I was wondering if anyone else happened to see what could either be a crack or casting mold on the intake manifold, under the newer bolt on the right side?
CJD @ Work

This thread was discussed between 17/02/2004 and 25/02/2004

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