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MG MGB Technical - Has anyone ever used this Weber carb setup?

I've never even heard of this conversion before. Don't worry, I'm not giving up my twin SU's. Just looking for opinions.

http://www.racetep.com/mgbmcch.html

Anyone know of anyone who's done this conversion?

Derek Nicholson

I havent seen it before, but contacted them and they said it only comes in a manual choke. Googling it seems to show that they use it on Harley EVO engines as an upgrade as well... Im pretty curious about the carb. I might give it a try. Anyone in need of a Weber 32/36, and a new zenith 175 ? Email me
James

For that kind of money, you can probably pick up a set of SU's and manifolds and get better performance. But I'm waiting for someone to step up and say I'm wrong.

Derek Nicholson

I built a complete inlet manifold system (manifold and inlet air tube with K&N filter) for a guy who had this conversion kit.

Prior to my work, he did run it as supplied on the stock Zenith manifold. The air filter does not fit well next to the brake booster and you have to dent it in to clear. I think he also removed the isolator system so that the carb just mounted solidly to the aluminum block. I also recall he said he had to mess with the mixture somewhat to make it work right (ran a little lean at some point if I recall).

He said it did work better than the original zenith setup once he tuned it in (he felt a definate increase in power).

Sean
Sean Brown

Derek,
Im not sure if you can get a well rebuilt set of Su's for that amount of money, for the Zenith b's you are also looking at a purchase of a header as well for the Su's. I really would like to know the difference between this carb and the 32/36 DGV. Because there is no gain in power with the downdraft, just reliability.
James

Why?
The single ZS is more than sufficient for up to 100hp on a real manifold if you can find one - at worst saw off the inlet part and throw the exhaust as far as possible. If you can read and follow instructions, you can make it work reliably with any of the known cold start options. The whole problem with the stock setup is the wretched manifold, and the sole advantage of this deal is that you get to keep the very worst part of a late B! So for $350 you get a new gizmo, that might work after you figure it out, on a manifold that doesn't work and is known to be prone to simple mechanical failure as well.
A twin SU setup doesn't need to be newly rebuilt, it will work fine if it's just not totally screwed up, and you'd be hard pressed to make it perform as badly as anything on the stock ZS manifold.
FRM
FR Millmore

FM,
I agree with you, I dont think I was explaining myself clearly. Its just good to have a carb that kicks over the first try and doesnt go out of tune. Im just thinking, ive always been a supported over the Su's over the webers, just curious to know how this carb works on the B, as comparted to the 32/36 downdraft, I had the downdraft on my car and definetly didnt see any gains, just reliability, would start right up in the dead of winter, I actually went back to a New Zenith because I just couldnt get the downdraft setup right, probably just needs new jets etc but I just got fed up and got a great deal on the Zenith. And yea I actually did buy one of the manifolds with the intake sawed off actually that I ran with the weber. Needless to say Im just very curious about the 45 carb. I might give it a shot and let you guys know. And it all depends on what used SU's you get, it gets expensive when you have to get them rebushed. Its always good to have a nice idle on a B and that carb just might be able to, I mean the 32/36 has that progressive throttle so you actually have less performace unless you throw the pedal to the floor and get both butterflys open than compared to the Zeniths 1 3/4s opening. Wonder if the 45 carb might be another option instead of the SU 44's on the supercharger from moss... Anyway Im just thinking out loud, its a monday at work and my brain is not up to par
James

Hi Guys,

One thing the Weber blurb ALWAYS leaves out is the fact that it is NOT a constant vacuum device (like the SU & ZS carbs) and therefore when you change altitude or the air pressure changes due to weather, the carb mixture goes off tune - to the point where, if set correctly at sea level, it will go so rich at 3000 feet that the engine will not run at idle!

So if you live on the plains then fine, but any mountains are going to need an SU or ZS.

If you can, change to a twin SU set up and experience a B as it was intended!
Chris at Octarine Services

Hey Chris,
Yea I agree, im just staying at sea level, you have a nice pair of SU's you can spare ? But the one thing I dont understand is that webers are a big aftermarket part for lots of cars (mikuni as well), including the 32/36 for the Jeep Wrangler, Ive never heard of mixture problems on Jeeps traversing off road w different altitude conditions.
James

Hey all,

A little off topic. I have a Mikuni PHH44. Looking for someone that has chokes and jets for these. Mikuni America does not help and send you to their dealers. The dealers only have parts for motorcycles and snowmobiles. Looking for 37 mm chokes, and some other jets.

Thanks,
Shareef
Shareef Hassan

You might just have to do an extensive google search and find where to get parts. I know a lot of the weber stuff comes from one place in the US and gets shipped around.
James

All,

For everything in life I use google. For MG's I use the forum. Unfortunately it never occurred to me to use google. First page there was everything I needed. Thanks James.

Shareef
Shareef Hassan

Chris-
Well said! SUs are the better option for everything outside of all-out racetrack-only engines.
Steve S.

Steve, I agree,

I also was emailing the guys at the website listed, and they said the clearance problem has been taken care of.

Now in regards to my situation, it goes like this. I have a new (sat on the shelf for a while) zenith on my 79 B, need a new alt and battery to get it up and running again. I had on a weber 32/36 and never got it running right, but the only good thing about the weber was it started right up in a second. Im looking to start using my B as a daily driver now. Hence my curiosity in the Weber MCHH carb. Now I could go with the SU's and switch out the manifolds and put headers on but im not just ready to do that yet. So for just pure reliability, a single barrel weber doesnt sound so bad at this moment in time. Maybe do a write up about it since it looks like we all have never used that carb before. Im going to search the Archive as well.
James

James-
At the risk of starting another great imbroglio, I'll say these things again.

"good to have a carb that kicks over the first try and doesn't go out of tune."
Yes, and both the ZS and the SUs meet the requirement. And they DO NOT "go" out of tune - they are PUT out of tune when ze leetle monkeys put they busy leetle paws in the works and fiddle, usually in an attempt to compensate for something else that isn't right. I check, clean and repair SUs when I first get or meet a car. Then they are left alone for many years of trouble free use. The only maintenance required is to clean the vacuum chambers periodically, and how often that is necessary depends on how good the air filters are. None or rat catchers mean cleaning often, very good like OE MGB filters let you go 12000 miles before cleaning. When the carb needs "adjustment" it will be because the engine has worn out. Bias needle cars may want new needles after 25000 miles, but will still run better than most replacement systems.
My experience with ZS is the same; these have two maintenance requirements, regular annual checks to be sure the screws on the outside don't fall out, and replacement of the diaphragm every few years.

"just reliability, would start right up in the dead of winter"
I expect that with both ZS & SU, and am very rarely disappointed. I did have an XK120 that would reliably start at 5degF, but not at all at 4degF, and my Austin America once refused to light at minus 37F until I heated the manifolds. Further, neither SU or ZS is prone to blocked jets, as are all fixed jet carbs.

Chris is dead on about the mixture changes with altitude and barometer. You think you are only at sea level? Look at baro pressures for the normal range of weather. I don't know where you are in NY, but on top of the Adirondacks, or in the New Hampshire mountains, in a storm, is very different from a sunny day at the beach. Bigger engines and less highly tuned ones simply do not reveal the drop in tuning efficiency as small ones do.

"...used SU's you get, it gets expensive when you have to get them rebushed"
The rebushing myth, like most such, has some truth and a lot of undeserved attention and belief. Yes, it's nice to have no slop. But, nearly all the wear normally seen is in the throttle shaft, very easy replacement. The little wear usually found in even the most worn carb bodies can be compensated in the carb setup. I have cared for thousands of SU/ZS cars over my 40 years of doing this commercially. I have NEVER rebushed a carb, and I have the shop, tools, and knowledge to do so correctly. I have seen a couple that people had rebushed "professionally" that were as sloppy as the average worn one, and worse than what they started with.

Blaming carb body wear for difficulty in performance is generally a way of getting around saying "I don't know how to set this engine up" Blaming the carbs for "going off tune" is a way of not saying "I didn't get it right the last time and now the new plugs I put in are fouled (or cooked)" If someone can't set up an SU or ZS system, they certainly can't set up a Weber, or anything else for that matter. In the rare case where the thing comes out of the box near to correctly set up, then you will no doubt get better running than you did with the screwed up predecessor. Furthermore, setup on a SU/ZS is a matter of adjustments without parts, if you have the right needle. On a Weber or similar, you have to buy arcane and difficult to get $$$ pieces, which you drop on the ground or into the engine.

Finally: "...dont understand is that webers are a big aftermarket part for lots of cars..." is a direct consequence of salesmen taking advantage of the facts of the preceding paragraph.

Yo, James, don't take it too hard, and if you are in western NY, bring the car and the box of bits by and I'll sort it - no downdraft Webers, as that's a waste of time. Playing with the sidedraft Weber could be interesting, but it won't be any better than the ZS/SU systems, and it could take a while.
Cheers,
FRM

FR Millmore

Hey FR Fillmore,
Dont worry about it im not taking it too hard, ive been listening to this discussion for a long time on this BBS and im a fan of the SU's and I agree with what your saying. I wasnt blaming the SU carbs or Zeniths for not being able to "set it Up" but they do need adjusting from time to time, and there is no way to compensate for a Zentih that needs its throttle shaft rebushed, I do have to differ with you on that one. But all this is a mute point because probably just before you posted this to the thread, I bought a pair of SU's off of Ebay...

I dont think I was explaining myself, as I was drowsy and bored at work when posting. The idea of the Weber for the Zenith is a nice idea, thats all. I didnt want to switch to the Su's and then have to buy a new exhaust system, but im going for it ! Oh and im on Long Island so yea pretty much sea level here. But there is also needle changes for the SU's and Zeniths for change in altitude... Albeit the needles are easier to change out compared to the webers... Anyway you will be seeing my postings and hopefully sensing my happy grin in the future after I get it all set up.

Oh I should probably post this in a different thread but what have people been doing with getting a new fuel cut off switch to replace the old one in the engine bay of the late model B's
James

James-
True that here is some variation in needle for SU/ZS at altitude, but the variations required for CD carbs are far less than for fixed jet/venturi carbs, which again require parts changes to correct. That's why the top racers - the ones who are always in the top 5 - maintain records of ambient temperature, humidity, barometric pressure, and altitude along with the right carb parts (jets and venturis on Weber) for each day, or even hour, of racing.
New throttle shafts will fix any of these to the point that any body wear can easily be adjusted for in 99% of the cases.
I repeat that once adjusted correctly, along with everything else, they do NOT need to be adjusted, with the sole exception of wear on the bias needle designs beyond 25000 miles. Just like the fixed jet carbs.

The "fuel pump cut off switch" is not a fuel pump cutoff, that is under the dash. The one in the engine bay is a rollover mechanical fuel shutoff valve, not a switch. It does not affect the pump. They leak and are commonly removed/bypassed, and I don't think they are available anyway - could be wrong on that part.

All smiles when you get your ride moving!
FRM
FR Millmore

Hey FM-
Thanks for the info...
James

Cold starting performance with a Zenith is usually just a matter of needle selection and proper choke function. On the single Zenith carb manifold conversions we've done, they all start up instantly with the right needle.

I'll agree with FRM, once a carb is setup, it's setup. Only wear of components (either in the carb, or in the engine) will affect the performance from there.

Sean
Sean Brown

Does anyone have any information about the sidedraft MCHH Weber Carb? I have an idea forming in my weak mind that if these are one barrel DCOE, I might buy two, build a manifold (with linkage) with a straight shot to the port, and replace my single 45DCOE. This would be for my vintage race car.
MGB 12

Like, perhaps using a manifold for HS6 SU's?

http://teglerizer.com/fi/MGB_twins/index.html
Derek Nicholson

I have run stock weber carbs, tuned for sea level, at above 7000 feet elevation - the CD advantage in this regard is, to say the least, overstated. Webers do have altitude compensation built in and it does seem to work.

I second that a Stromberg can be an acceptable carb, and the problem is the manifold. I DID saw off the manifold, and tried running a single Stromberg with a decent exhaust header, and it worked! Vastly better than stock. Revs great, delivers good power, etc - proving once and for all that the Stromberg wasn't the problem, the manifold was. So I think this setup replaces the wrong part of the system. Granted, Strombergs aren't the best carbs ever, and this may be an improvement, but any decent project to raise the power of an RBB requires trashing the stock exhaust manifold.
Sam

This thread was discussed between 26/02/2007 and 11/03/2007

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