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Re: Best Carbs for MG???

Subject: Re: Best Carbs for MG???
From: Scott Fisher <>
Date: Sun, 02 May 1999 09:17:49 -0700
Don Cobb asks:

> What is the lists opinion when it comes to the best carburetor
> for the MG?

Actually, Don, that's almost as deeply religious an issue as what is the
best M.G. for a carburetor. :-)

I can weigh in with experience on SUs and the Weber 45DCOE, and on Bs
primarily; on my first Midget I only ran the stock SUs.  SUs are
traditional, which is three out of four points in their favor; they're
easy to work on, which is both good and bad; I say that SU carbs are
like Unix -- they're expert-friendly.  They provide decent performance,
good drivability at low RPM levels, and good fuel economy.

And then there's the Weber 45DCOE.  No, this isn't the downdraft kit,
this is the twin side-draft, legal-only-for-racing-vehicles carb that is
somewhat legendary.  

On a performance-tuned engine, the 45 is superior to the SUs in every
way, including low-RPM drivability -- assuming you've tuned the carb and
the car for that.  On my "hot-rod" MGB motor, my friend Chris Kantarjiev
and I dialed in the Weber that Mark Bradakis originally set up for me. 
When Chris was test-driving the car with me after we got the idle
adjusters set for a really lovely, smooth, low idle (on an only mildly
lumpy cam, a Piper Blueprint 285 -- highly recommended), we were
puttering along at 1000 rpm in fourth gear, doing 25 mph or whatever
that worked out to (3.9 rear but 185-60 tires, which worked out to the
same ratio as a 4.1 rear with stock tires).  Chris floored it in fourth
at 1000 RPM and it just pulled smoothly, without flat spots or hiccups
or bobbles; he gave up around 4000 RPM which was fast enough for
traffic.  Another time, and on a clearer/safer road, I saw just shy of
7000 RPM in fourth in the same car.  That was pretty much the useful end
of the powerband for the cam, head and valve springs we had in the
engine then, and it was slower than it would have been on the taller
stock tires (I think I calculated it out to about 105 mph, though the
speedo was pegged at 120 and bouncing) but it was pretty exhilarating

Would I do a Weber again?  Unquestionably, though it's worth pointing
out that on this hot motor, I ran the '71 SUs with stock spring-loaded
needles, adjusted two flats richer at idle, and even used the stock
button-in-the-middle butterfly plates.  The Weber *was* better,
especially at the top end of the powerband (5000 RPM and up) but it
speaks well of the SUs that they were able to cope with such a vast
change in their original operating circumstances.  

So... don't ditch the SUs on a whim.  Look up Roger Garnett's articles
in the archives, or mine, or go to a tech session with your local club. 
It's worth learning to make SUs work before you toss them out.

If you've got a 75-and-later with the single Z-S carb, I can't help you;
I've always owned twin-carb M.G.s (or at least M.G.s that started out as
twin-carb cars).  And I'm planning on leaving the SUs on my "next" M.G.
at least for the first year or so, while I get everything else dialed in
nicely.  After that, who knows?

 -- Scott Fisher
    Sunnyvale, CA

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