Unfortunately, by the time B-L was fitting Z-S carbs (along with the cat and
the other emissions control stuff) to meet the smog laws, testing by
analyzing the exhaust gases had become standard practice. The workshop
manual, in concluding the carb tune-up section, says to adjust the mixture
until the prescribed CO levels are reached (with the air pump out of the
system, surprisingly).
So, adjusting the carb the old fashioned way (by adjusting the mixture for
the highest, smoothest idle) and testing by raising the piston a small
amount do not necessarily work with a Z-S carb. We find that final
adjustment of the carb with the 4-gas analyzer in the tailpipe is really the
best way to obtain both the smoothest possible idle and the cleanest exhaust
gas - and the two are not necessarily the same setting! Depending on the
condition of the camshaft lobes (remember - the hot catalytic converter has
been baking the oil off the camshaft every time the engine has stopped since
that camshaft was installed, meaning excessive lobe wear until fresh oil
arrived at the cam after the engine had been started and run for a few
seconds), the valves and rings and the ignition system, it may just not be
possible to get a truly smooth idle with this ultra-sensitive carburetor.
Lawrie
British Sportscar Center
-----Original Message-----
From: Eugene Harrison <eugh@2xtreme.net>
To: MGS list <mgs@autox.team.net>
Date: Wednesday, November 17, 1999 8:02 PM
Subject: Re: Z-S carb problem
>Thanks for all the responses!
> Lawrie was right on about the intake tract needing to be
>installed for the Z-S carb to function properly. I readjusted the needle
>for slight increase in RPM (piston lift method) then reassembled the air
>cleaner, hot air flapper (bong bong bong, just love that lovely piece of
>brit engineering), and now she reves sweetly to high RPMs.
>Unfortunately, it still has a bothersome stumble at idle. I have had
>cars fail the California smog tests with this stumble. By blocking off
>or otherwise removing components, I have eliminated all other sources
>of vacuum leaks except the carb itself. I will try using carb spray
>around the throttle shaft next to check for leaks there. Are all Z-S
>carbs like this?
>Thanks again to all that responded.
>Eugene
>
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