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MG MGB Technical - NAS 1977 MGB Carburettor change...options/advise ?

Hey chaps....have a 77 B untouched and original but clearly struggling with it's Stromberg carb and all the US mandated emissions garbage that's on the car....airpump/gulp valve/cat converter, which is shot etc etc. The manifold is the 1 piece with EGR valve. Question....if this was your car...what would you fit? I want more power, though not 100bhp more. Weber/2 SUs/single HS4 SU? What manifolds do I need....and am I OK for New York State inspection where cars over 25 are apparently exempt from emissions inspections?
P J KELLY

PJ --I have a 76 B which had the single Stromberg carb --I upgraded to twin SUs HS4 from early 70s car --You need the intake manifold--the exhaust manifold of similar years and its not too complicated to do.There is a big improvement in the car.My car when I bought it had already been stripped of the air pump etc so I wasnt faced with that.
The archives are full of threads on this and many say that you can meet emission standards with well tuned SUs.
I recommend it
All the best --Gil
Gil Price

It's just amazing how all this 'stuff' can make these cars run really bad. Especially if they are a little worn.
I switched over to twin HS4's, a header, no air pump, or EGR, etc.
Well OK, I also rebuilt an earlier engine, ['72] raised the compression, port and polish the head, better reground camshaft, balanced, etc.
Really runs well with plenty of power.
You won't be sorry.
Safety Fast
Dwight
Dwight McCullough

I recommend the Weber downdraft 32/36 DGV. It's a simple installation. Use the manual choke version, not the water or electric choke versions. I have a '77 and it starts first time, every time. A fuel pressure limiter is needed because the electric pump will overpower the Weber and you will need a used exhaust manifold from a 74 or earlier model. Change the distributor to a 25D4, use a new vacuum advance mechanism, install a pertronix breakerless ignition, and you're ready to rock n roll.
Charles Edwards

P.J. as Charles suggests; Webber, 25D4, pertronix, header. Just completing my 77. Amazing difference.
I purchased a stage I upgrade from Brit-Tek which gives you a little more. Cam, timing chain, lifters etc. Haven't put those in yet (A winter project).
I am extremely happy with The carb,header, dist, and exhaust. Can't wait to add the cam.
Dan H.
Dan Hanson

PJ. Go with the twin SUs as a first choice. Purchase a new set directly from Burlen in the UK. I prefer the HS series to the HIF series myself, but opinions differ on this. You will need to get the applicable intake manifold, heat shield, spacers and an exhaust manifold and early style head pipe. You will need to use the K&N conical filters with this conversion and install a take off for the brake servo into the intake manifold. Make sure you get the proper intake/exhaust manifolds as a matched set. There were two different thickness of flange. One for the HS series and one for the HIF series as I remember it. Make sure both the intake and exhaust have the same flange thickness so they will seal properly to the cylinder head.

As to the Weber 32/36 DGV. Good carb, meets Arizona emissions test standards and is exceptable to the local testing station which will only allow one carb. Not, however, in the same performance range as the twin SUs due to the smaller carb throats (venturis). The stock carb is also a progressive opening with the second barrel opening at about 3/4 of the way to full throttle. The Weber 38/38 with simultanious opening throttle plates might be a much better performance carb, but it is relatively recent on the MGB scene and not too many people have tried it yet.

As to dizzies, either a "Euro Spec" from Brit Tek (if they have any left) or a John Twist rebuild of an early MGB 25D4 should work fine.

I have two cars with the Weber DGV, but am rebuilding a set of HS-4s to install after the next emissions test. Les
Les Bengtson

PJ - I have a pet theory that you will get most of what you're looking for by just switching to a better ignition system, like the Euro-spec distributor that Les wrote about.

I did some checking a little while back, and the 1980 Rubber Bumper MGB was as fast, and had the same torque, as the last chrome bumpers. (13.4 vs. 13.3 sec's 0-60 - per Road & Track). The 1976 & 77's though, were bog slow at over 18 sec's.

What changed was the ignition system. I believe (and this is just a hypothesis) that the factory was new to emissions in the mid seventies and using points and condensers, they retarded the timing and took a lot of the power out of the powertrain. With more advanced (pun unintended) electronic ignitions, they restored nearly all the performance, despite the added weight, height, etc.

If you want to conduct an experiment (and save a few bucks) you may want to install the distributor FIRST, and then see how it runs. (It isn't the electronics, per se, but the advance curves and settings emissions vs. not).

Some caveats -

The Z-S is no great shakes as a carb. I hear the choke often doesn't work and also there's a plastic fuel line that's prone to cracking after all these years. (Vicki Brit used to have a single SU conversion, but I don't see it in their catalog anymore.)

This recommendation only gets back to stock chrome bumper acceleration levels. If you want more, and willing to spend it, then carbs, compression, cam, etc., are all in the mix.

This is just a theory - if you had no intention to swap the distributor, then just go for the carbs.

But always remember the rule of thumb "90% of all carb problems are electrical".
John Z

If you wanted to do the least amount of work, yet upgrade carb, etc. Go with an HIF44. It will replace the Z-S, yet utilize the same intake/exhaust headers. I've been around cars that have converted to the HIF44 and it's made a difference. Also definitely switch out the distributor. John is pretty much on the money as far as what he wrote.

Granted, it's not going to make it an absolute rocket, but it should improve performance some and probably make it a bit more reliable.

Robert
Robert Rushing

Les is right about the Weber's and their performance in MGs. I did the Progressive 32/36 DGV thing many years ago and I was always frustrated with it. It was probably close to the performance of the HS-4s at lower rpms and usual around town puttering, but it would always run out of steam as you pushed it hard to accelerate. The problem was simply that the progressive DGV lacked sufficient air flow to also pull enough fuel and the engine was starved and performance flattened. If the 38/38 Weber is anything like the one on a '61 Fiat I once had, it should provide a much more satisfying experience if used with correctly setup distributor.

Altho I run with a pair of Burlen HS-4s, Robert and John Z's advice together may produce at least as good a result. There are some advancements that SU gave the HIF series which may be of value to you. And the Twin HIF setup from the 70s could give you the best of all of these. Some folks on this BBS have given some good reasons to choose these over the HS-4s, so a little research thru the archives and in a couple of good SU books may help you decide.

Bob Muenchausen

John Z. Interesting theory. While no wheres near as competent to comment on this as you are, it does seem to explain what I have seen with my daughter's 77B. Unfortunately, having been taught to drive by "dear old dad" she tends to drive as I do. I found it very interesting that her 77, with an aftermarket dizzy and a Weber DGV was very similar in performance to my 68 GT. The GT would perform slightly better, but not a great deal. Originally, I thought it was the older engine in the GT that was the cause of this. However, over the years, as I have gained more experience, I tend to agree more with your position.

Currently, it is my belief that the major "problems" with the RB cars is that the Z-S is a piece of junk (this means that I cannot tune it properly to pass Arizona emissions testing like I can a Weber 32/36 DGV or twin SUs), the very slightly lower compression ratio (the early cars had about 8.8:1 while the 18V engines had 8.0:1) and the distributor advance curve is not the best suited to maximum performance.

Last year, I rebuilt the engine on my 79. I used .040" over pistons, a CB camshaft and the Weber 32/36 DGV and a Mike Brown modified cylinder head. When tested for emissions, the car was well within the required limits. However, the car does not perform as well as I should like. When the second barrel of the DGV opens, the car responds wonderfully. With partial throttle, it is relatively tame. I suspect my spare set of HS-4 carbs, installed after the next emissions test, will completely change the character of the engine.

I tend to agree with your theory that MG was just beginning to understand what was required to provide both performance and meet the US emissions standards. The US car makers were in a similar situation at that time. Brian J. Moylan's book, "The Story Behind the Ocatgon" tends to support this belief. Moylan states that by 1980 the MG was capable of meeting all current and projected US emissions testing standards. Thus, the common theory that the MGB died due to its inability to meet US legislation is severely in doubt. The Brits could, and did, meet all of the US criteria. It seem clear that the decision to take the MG out of production and close the factory was motivated by something other than "US regulations". Les
Les Bengtson

Thank you guys sooo much for your opinions and responses...really excellent BB discussion and for a new MG owner like me who is very technical, but never had one of these little cars before, I really appreciate saving me re-inventing the wheel here. It looks like twin HIFs are the best way to go with an older dist/standard older exhaust manifold and exhaust system. Will update on how it works out.
Thanks again
Pete
P J KELLY

PJ: HS-4 carbs are just as good as HIF's and cost much less new. If you buy HIF's be sure to get the ones that DO NOT have the poppet valve on the butterfly. Those nasty little things cause problems with idle and airflow. If you can combine new carbs with a Piper BP270 cam and ignition mods suggested above, you will get a vast improvement in engine response and performance.
Terry

further: While I would recommend SU's as the best overall, the Weber is the easiest and cheapest-everything you need comes in the kit except for exhaust manifold/header. I've used the DGV with good success and the same overall performance as SU's. As Les reports I got good driveability and economy at lower revs/throttle openings and a real kick when the second barrel opens up. When I want fast acceleration from idle or any engine speed I just floor it and the response is excellent.

Les: what jets are you using? With your extensive mods a big change is warranted. If your mixture screw is more than 1 1/2 turns out that's a good flag to jet up.
Terry

Les - thanks for the note & vote of confidence. Frankly, I don't FEEL confident. I have seen some data and have tried to make sense of it, but I'm not knowledgable enough in ignition particulars to nail it down.

All I do know is that the rubber bumper B was initially bog slow, and then clawed back in torque and performance (and, to a less extent, horsepower), over the last 5 years of its existence. And the only change near I as I can tell was in the ignition.

Something to keep in mind though, was how bad things were for car enthusiasts in the mid seventies. MG suffered, but then everybody pretty much "sucked", too. Only in the mid-Eighties or so did fuel injection get scienced out enough to begin to meet emissions, get reasonable fuel economy and restore a measure of performance, until we come to today, where we really have the best of all worlds - unless you want to tinker with the system yourself!
John Z

Terry. My DGVs are stock as supplied for MGB use. Yes, the idle mixture screw is about 1 1/2 turns out for best performance and just under that for best emissions. My "problem" is myself. I have played the emissions game here for many years. I have set my cars up to meet emissions standards and have, to the best of my ability, tried to keep the cars at that state of tune.

My conclusion, now, is that I am one of the few people driving older cars who is doing this. The more I find out, the more I am convinced that a large number of people are only playing this as a game. They are tuning for emissions, then, after the test, retuning to a better performance tune. Many are registering their cars outside of the area where emissions testing is not required and still driving them as I drive mine. The State is playing games, dropping emissions testing standards far below what was required when the cars were new, forcing many people to either sell the cars out of area, quit driving them or to look for some form of "dodge" to keep them on local roads. So, I am going to begin to do some experimenting to find out what is actually possible and am going to be less concerned with meeting the exact letter of the current regulations. Hence, some of your suggestions are areas I will experiment with. Thanks, Les
Les Bengtson

Les, you have that right...I am having the worst timme trying to get my 85 Saab Turbo thru. New York enhanced emissions. Tha car is 18, runs and drives like new, but JUST fails on Nox...last year it would have passed easily...the levels permissable have been halved since last test...and these levels apply to ALL cars up to 25 years old. Lucky my MG is 26. But here's the real kick in the pants....my Land Rover is exempt from the dyno test...as are all 4*4s. What a bunch of BS...
P J KELLY

I installed HIF4 carbs and am very pleased with the performance, appearance, maintenance...everything. I have tapered K&N air filters.
The carbs, heat shield, intake, exhaust, choke cable, accelerator cable, and everything except the air filters was obtained for under $300. The cables were new, the rest was used but in good condition.
Randy Olson
1977 MGB
randy olson

PJ - I have tried every combination known to man - the twins SU's the Stromburg that came with the 77B and they all had major drawbacks. My final solution was to rebuild the engine and port and polish and cc the heads and have the engine balanced and blueprinted. The unit I chose was the Pierce and Weber combination from Moss - that turned out to be a little rough. I put the car on the smog machine and found out tht the Weber was far to rich - I then found the smallest jets that I could find and gradually driled them out until I hit a good combination that would not only perform well but also pass smog. Another thing I did was adjust the secondaries on the the Weber so they would kick in a little early along with adjusting the timing to 15 degrees before TDC to coinside with the hot cam. I am able to run at close to 6000 RPM before it starts to starve and the power curve from 3000 to 5500 is great! While crusing at 75 MPH and mashing the throttle all the way down you can feel the push and hear the great sound of the secondaries kick in. Also tuning the weights in the distributor also helps. Good luck.
JC Nelson

For those who have cars NEARLY old enough to be exempt from emissions testing, I have an interesting story. First off, let me mention that my MGB could only pass California emissions testing after some tuning acrobatics, and then only at the third attempt and while I leaned on the throttle shaft.

When I relocated to Washington state, I discovered that 25 year old cars were exempt, but (in 2001) my 1976 was not exempted because the exemption in 2001 applied to 1975 model years and older.

To cut a long story short, I questioned the basis that they could interpret a "25 years or older car" as all those built in a certain model year. After legal acrobatics (preferable to tuning acrobatics I decided), I showed them that my car was over 25 years old, and that they were being quite arbitrary in requiring ALL 1976 cars to be tested.

I am not sure what a judge would have said, but after I had made enough of a nuisance of myself going up the government heirarchy, they relented and exempted me.

The significance of this in my case was that I could drive the car 6 months before I would have been able to otherwise. So if your car is just coming up to the exempt age as dwetermined by model year, this might be a tactic to consider.
Daryl

Soooo....got a new catalog from Brittek today and they have kits with Piper cam/Weber/manifold/Peco header & exhaust etc etc ...all new for about $1200.00. My question is do I really need to drop the oil pan and pull the oil pump to change that camshaft out????
P J KELLY

This thread was discussed between 08/09/2003 and 16/09/2003

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