Lawrie: Do you mean that Twist misspoke when he made his conflicting
recommendations?
Frank
British Sportscar Center wrote:
> With all due respect to Bob Holton (who posted a separate response to
> Frank's post and who may have more years of experience with Z-S carbs then
> me, for all I know), a Z-S carburetted MGB engine will start but will not
> run "just fine" without the air cleaner on. If it does, then it is not tuned
> correctly! As the Moss book says, these are very sensitive carburetors
> (note, I didn't say efficient!) and they are set up to comply with emissions
> requirements with the air cleaner in place. As such, they are not delivering
> a proper mixture down that convoluted intake manifold when the air cleaner
> is off.
>
> John Twist's advice about testing the mixture strength by raising the piston
> a little bit is very applicable to SUs, but not to Z-S carbs. With a Z-S,
> all you can really do is adjust the mixture for the fastest, smoothest idle
> (as always, after making sure the ignition system is in perfect working
> order and that none of the emissions valves are malfunctioning). Our 4-gas
> analyzer shows that very small adjustments, via both the needle adjustment
> and the trimmer screw on the side, make a noticeable difference in the
> exhaust gases. This, of course, also tells how efficient the engine burn is.
> So, for optimum engine performance, it's best to have the final adjustments
> made - with the air cleaner in place - by someone with a 4-gas analyzer.
>
> Lawrie
> British Sportscar Center
> ----- Original Message -----
> From: "frank krajewski" <frankk@intap.net>
> To: "MG List" <mgs@autox.team.net>
> Sent: Thursday, April 04, 2002 12:31 PM
> Subject: ZS Confusion
>
> > I am down to fine tuning the motor in my 1980 B, which I totally rebuilt
> > over the winter. Thanks to Lawrie I now know which way to turn the
> > special ZS carb adjusting tool for leaning and enriching the mixture. I
> > am a little confused however when I attempt to follow the instructions
> > provided by John Twist, whom we all agree is one of the gurus (along
> > with our own Lawrie) of MG repair, on page 85 of the MGB 16 Moss
> > Catalogue. At the top of Twist's guidlines is the sentence, ""Lift the
> > piston slightly. If the idle speed rises...etc". That is great and it
> > assumes the engine is running or how else can the the idle speed vary at
> > all? To lift the piston in the ZS carb entails removal of the air
> > cleaner to allow access to the piston. Now my confusion, at the bottom
> > of those same guidelines (Item #3 under "Running Lean") there is a line,
> > "The Stromberg carburretted MGB will not run with the air cleaner
> > removed...." OK, what did I miss? Let the flaming begin....
> > Frank "Swamp Yankee" Krajewski
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