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MG MGB Technical - Weber carb

I am thinking of replacing my su carbs on my 18gb motor with a weber dgv. Need pros and cons on conversion.
E Maneely

E Maneely,

Opinions vary on this, and are often strongly held. However, there are many that would agree that changing the single Zenith/Stromberg to a Weber DGV is an improvement, while changing twin SUs to a DGV results in less performance.

I bought a 77 that was changed from a single to a DGV before I bought it, but I have not fully sorted it to form an opinion. And, even when I do, I will not have the "before" experience for comparison.

Personally, I like the SUs.

Charley
C R Huff

I have SUs on my 72B, no problems, and curiously the above response triggered an experience from a test drive last night.

I test drove a 77B that has the Weber carb on it. The car runs just fine, but it sure appeared to lack the zip my 72B has with the twin carbs.

The pollution equipment is off of both my 72B and the 77B I test drove, so the engines should be about as equal as possible (mine has a recent valve job).

Of course I have no idea how well tuned the 77B but it test drove just fine, just felt "doggy" - a noticeable difference in response when putting pedal to floor.

Of course there may be issues with the Weber. I noticed a vacumm fitting on engine side of base of Weber that was not connected to anything. Also the vent from the top of the valve cover is not connected to anything, and the vent hose from the side of the engine case goes to open air. Whether any of these contribue to poor fuel performance I don't know.

The end thought is, the Web 1800 77B felt slow in acceleration to my SU 1800 72B.
R.W Anderson

Hi Guys,
When i bought my 64B Roadster a few years ago it had a weber fitted with vacum advance disconnected but it never ran 100% so i connected the vacuum again which made it even worse.After talking to a MG mechanic i was told to disconnect it again and set the timing at 13 degrees ( other people will probably have different ideas on this ) and retune the carby. Apparently there is only about a 3 degree movement in timing so it won't be a problem. I beleive guys who race older cars with webers also do the same thing. Anyway my car now runs a lot better and has lots of punch once about 2500 rpm is reached but a little sluggish at bottom end and as the weber draws so much air it sounds like a vacuum cleaner (awfull). In essence I am seriously thinking of fitting SU carbs simply because i don't like the sucking sound from the weber and the sluggish bottom end.
Personal choice.

Spoggy.
Dave ( spoggy )

One word answer.

"Why?"

Few things are as reliable and long lasting as an MGB's dual SU's. If your SU's are sound, then have them set up properly. If the throttle bushing is worn, have the bushing redone. If you don't think there's enough oomph, then have the head set up by Peter Burgess or Sean Brown.

DGV Webers are fine in comparison to Strombergs, but are flat at low rpm in comparison to constant velocity SUs. I believe the Weber is comparable to the old 2 barrel carbs used on Vegas and Pintos. Both of those cars could have benefited from a set of SU's.

If you decide to change anyway, put the old set up on eBay. Someone will snap them up - replacing their old Weber.
John Z

Keep in the back of your memory bank. I hit the parkway last year and was only able to complete the first half of my journey due to altitude. At 3500 ft to the inch, I started fouling plugs. No adjustment would help and even removing the air-cleaners for more air. I was headed south to the end at 6700 ft+. Have been told since that I should have taken leaner needles and made a change. I am sure there are lots of other ideas and (1) was going to weber. Not A Chance, when it runs good 100% of the time below 3500ft, I'll stay below 3500ft. Or take leaner needles the next time. On another note, I am parting out most of a 75-B, yell if you need anything..Steve C.
Steve C.

Steve C,

I think there must be something wrong if you couldn't get over 3500 feet. I drove my 68 GT to northern CA from KY on the southern route. Continential Divide, NM on I-40 is over 7000 ft., and I think some points near Flagstaff, AZ are higher. I cranked my SUs 2 or 3 flats leaner and had no problems at all. My base altitude is around 500 ft.

Charley
C R Huff

I had someone tell me the same thing. Maybe I need to start another thred with this topic, it could be something else going on that shouldn't be.
Steve C.
Steve C.

Steve C,

Yeah, it might be worth another thread. A few days ago I saw someone comment that SUs are self compensating for high altitudes. I suppose this is because the air pressure gets changed on both sides of the piston. It was the first I had heard that, but it might be so.

Also, I've had SUs since back in the sixties on big Healeys, TR3s, and Minis, and I've run them smack over the Rockies many times through Colorado, Utah, Nevada and Wyoming. I am reasonably sure that I have had them up to 10 thousand feet or more, and my base was either KY or CA.

An old girlfriend of mine pulled a trailer from KY to CA over the Rockies with an 850 cc Mini, and the GVW was more than double the weight of the Mini alone. I'm not saying it was fast, but she made it.

Charley
C R Huff

Interesting thought on altitude guys but what are your thoughts regarding the weber in that situation

Spoggy.
Dave ( spoggy )

Vacuum advance is used for improved cruising economy, something which racers aren't particularly interested in and not having vacuum advance makes them much easier to set up on a rolling road, having one less dimension to take into account, and this applies to many different carb types.

It always ammuses me when I see vacumm-less distributors advertised as 'performance' distributors, as if not having vacuum advance is in itself going to make it go better.
Paul Hunt

Oh yes, if you have a vacuum port on a carb or inlet manifold and you don't use it, it *must* be sealed off.
Paul Hunt

Spoggy,

I'm not too savvy on Webers, but I think you can't change their air/fuel ratio without changing jets. Therefore, I think the SU would be the better choice for changing altitudes since you can adjust the main jet to lean it at altitude.

Charley
C R Huff

NOT going to recommend any weber on a B. I tried both a 32/36 and even a 38/38. Twin HS4s outpaced both webers easily on my car....the weber only works over 2500 rpm...anything under this and there is no torque...and the intake is noisy too.
P J KELLY

This thread was discussed between 30/06/2009 and 08/07/2009

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