The change is a good thing.
The ZS is a 1 3/4 inch single barrel. And has lots of problems, not
least of which was the water choke. They are generally hated by the MG
community. They were put on for emissions along with the Catalytic
converter.
The SU carbs are 1 1/2 inch single barrels. 1 sends fuel/air to
cylinders 1 & 2, the other to 3 & 4. For the most part. There is
a tube in the intake manifold to "equalize" the flow. But if the
carbs aren't tuned together, they don't run well together.
Performance is the reason. You get a lot more horsepower from
an earlier engine than a '75 on engine. Horsepower numbers are
foggy... Ok 68 for the ZS and upto 98 for SUs. Though HIF vintage
(71-74 1/2 or so) were rated in the 92HP. If my memory serves.
Somewhere in there, there was a 'how horsepower is calculated' change
so these numbers aren't exactly apples to apples.
The latest issue of "Grassroots Motorsports" (Feb '03) has a nice
article on a trip to the Dyno for a RBB, I even think it's a '78.
To sum up, the SUs were substituted to increase performance, reliability
and tunability.
That's if the SUs are in good shape. They wear out too, but rebuilds on
those are well docuemented and well understood.
Paul.
theodore anderson wrote:
> Hi:
> I recently became the proud owner of a 78 MGB. My mechanic informed me
> that the original carb was a Zenith Stromberg and that alterations had been
> performed so that the configuration is a pair of SU HIF carbs.
>
> Dumb questions:
> 1. Is this change a good thing?
> 2. Are these single barrell carbs?
> 3. Why would two carbs be desirable on a 1800cc engine?
>
> By the way, the whole car runs great. Amazing what you can buy off eBay.
>
> Ted
>
> [demime 0.99d.1 removed an attachment of type image/gif which had a name of
>IMSTP.gif]
>
> [demime 0.99d.1 removed an attachment of type Image/jpeg which had a name of
>BackGrnd.jpg]
--
Paul T. Root E/Mail: proot@iaces.com
600 Stinson Blvd, Fl 1S PAG: +1 (877) 693-7155
Minneapolis, MN 55413 WRK: +1 (612) 664-3385
FAX: +1 (612) 664-4779
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