American MGB Association Message Board

Technical Area => Upkeep and Performance Hints => Topic started by: amgba on November 14, 2020, 05:18:32 PM

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Title: Carburetor Selection
Post by: amgba on November 14, 2020, 05:18:32 PM
I've driven MGBs for 50+ years with dual HS-4s, dual HS-6s, dual HIF-4s, single Weber 32/36 downdraft, and dual Weber DCOE 45 sidedrafts.

Carburetors should be selected based on objectives.

If it's advice you're looking for, the best I have is: use your MGB as a daily driver! That will "blow the dust out of it," keep it in good condition, make you aware of its needs, force you to maintain it, make you appreciate it, and give you plenty of fun, joy, and pride of ownership.

Naysayers and purists will urge you to keep the SUs. It's a decent carburetor but, other than cool looks and originality, there's nothing magic about them.

The SU was invented in 1904, so don't believe the uninformed who tell you it was designed for the MG.

It was simple and cheap and that's why it was selected. They are easy to tune, slightly difficult to keep synchronized, and in many cases have to be frequently re-tuned (usually a fairly easy job).

Because most of them are very OLD, they are often worn and require rebuilding.

The Weber downdraft which is a two-stage carb comes in several models (with throat sizes of 32/36, 32/38, 36/38, 38/38, etc.). Under normal driving conditions you are using just one pump and throat, resulting in excellent gas mileage. When you need acceleration or just thrills a further push on the pedal engages the second stage for a surprising zip. It's slightly more complex to set up than a single HS-4 but about the same as two of them. If it's in good physical condition, it's quite stable.

Many people confuse the Weber downdraft that you're considering with the much bigger, MUCH higher performance potential DCOE sidedraft which is a very serious carburetor that, in pairs, has four times the fuel-air delivery potential as dual HS-4s.

I currently have a really souped up, bored, balanced, high compression, '78 with racing spec internals, street-racing cam, crossflow head, tuned DUI coil-distributor, roller rockers, and much more. It's a little rocketship to drive.

I also have a '73 with dual HIF-4s and it's a ball, as well. It has the usual MGB slow reality, fast feel, and thrills to drive.

I drove one with a Weber 32/36 for several years and was quite satisfied with it ... and I have a bit of a heavy foot and love speed-shifting through the gears. It was a solidly driving car with excellent fuel economy and handled exceptionally well on numerous cross country road trips and as a daily driver.

In general, I avoid asking people's advice: the purists will ALWAYS tell you not to "ruin" it by making any changes; everyone else will tend to advocate for whatever they have; many of them never tried anything else and the few who did might have never learned how to properly use the alternative product or system.

Instead, I ask specific questions and make sure other members know am seeking information and not looking for opinions. Hope this is helpful.

Barry Barnes

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