On 28/03/2021 21:05, Tim+ wrote:
Fredxx wrote:
On 28/03/2021 18:14, wrote:
In message
"Dave Plowman (News)" wrote:

In article ,
Brian Gaff \(Sofa\) wrote:
How will this new extended low emission zone in London affect these
older vehicles? One assumes the charges are applied via apnpr, in which
case I guess if you stuck a new or modified engine in that would not be
recognised. Brian

Being an injection engine (but before catalytic convertors) it already
produces fewer nasties than many diesel vehicles that were fiddled to pass
the type approval tests. And there are millions of recent vehicles like
that on the roads.


My 1970 2a Land Rover used to fail the emissions test at MOT time even
with a new engine, new ignition system and brand new Weber carburettor
I always had to tweak the carb mixture too weak so it ran like a bag of
**** at MOT time to pass and then turned the carb mixture screw back
aftewards so it would run properly again.

In the good old days simply slackening off the timing would allow for a
weaker mixture at tickover. More volume, so less dilution.


Um, how did that work? Changing ignition timing changes neither volume or
dilution.

By a combination of retarding the ignition and increasing the idle
volume in tandem meant you kept the revs at a 'normal' level. Sorry,
should have clearer.

One reason idle mixtures tend to be on the rich side is to prevent
misfiring. It was said to be down to dilution with retained exhaust
gases. The more volume, the less the dilution.