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Re: Alternative carburators to the SU?

To: "Rollins, Dan" <>
Subject: Re: Alternative carburators to the SU?
From: Robert Allen <>
Date: Mon, 16 Jun 1997 19:42:36 +0100
Rollins, Dan wrote:
> My problem is the carburators were tired out, so I decided to rebuild
> them.  I discovered a PO put HIF4 carbs on it.  I have decided to
> revamp the ignition and fuel systems (electronic ignition, new carbs
> and fuel feed lines, etc.)  I have been considering getting a Weber
> downdraft.  Does anyone have any experience with these carbs?  Do
> they give any added power and reliability? (Not that the SUs aren't
> reliable . . .) :)

IMHO the Weber sidedraft is a great carb if your engine has been
seriously breathed on. But, paradoxically, it may not be so hot with the
mighty 'B' (and 'A') series motor. The problem is the siamesed intake
ports, i.e., the adjacent cylinders share an intake port. The Weber
sidedraft likes one intake pulse per venturi.

You _can_ make the Weber work just fine on the 'B' motor it just takes
some fiddling. Many 1000's have been installed, I'm sure, and someone on
this list will be happy to read you the numbers off the air and fuel
jets, the emulisfier tube, and the idle jet.

Sidedraft DCOE Webers will never pass emissions because they are pretty
dirty at low RPMs.

The Weber downdraft is not a high performance carb and has never been
advertised to be. However, the 'B' motor cannot claim high performance
in a stock configuration so they are a pretty good match. One of the
problems is not enough room for a decent sized air cleaner. 

The downdraft carb is highly reliable and not very finicky. You can buy
the Weber downdraft with the ECO number for emissions legal. The '67 BGT
I had with this carberator had it's problems but two pumps on the
accelerator and it started every time, any time, no matter what the
weather. It had an electric choke and everything worked great -- for a
stock motor.

I'm not current on hot 'B' motors. When I was studying hot 'A' motors,
they often went with a single, large SU (like a 2 inch) which provided a
fairly even intake pulse with the the siamesed head. But those were 1275
motors and may not apply to the 'B' sizes.

Also, the dorky looking log manifold is fairly efficent with this head
in stock and slightly modified form. Plus there is enough material to
grind it out and smooth the flow with larger carbs -- but I don't know
the practical limit.

There also some folks that can flow your standard carbs and get decent
performance out of the stock SUs.

I don't know anybody that uses the phrases "high performance" and
"Zenith Stromburg" in the same sentance. (Hey? I did! Oops!)


Bob Allen, Kansas City, '69CGT (3 DCOE Webers), '75TR6 (2 Strombergs)

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