"It happens in real life that people make that error, swapping carbs between
engines of different sizes. My GT6 had red (IIRC) needles but needed
yellow. It took me a long time to learn this lesson."
Evidently. The lessons not over yet . The Springs are Color Coded not the
Also I'm familiar with the Carb swapping in real life. Have done many
Conversions, Weber, Dellorto's,
SU's, Just never swapped any Zenith products onto anything except replacing
Land rovers Solex with them.
Worse Carburettor, just Cheaper than finding a good LR Solex.
Jim Wrote: Previous post:
"Also consider the springs. They must match the expected airflow. If
they were from a smaller engine, they will be too soft and the
pistons will top out too soon. This will make the mixture too rich
at higher flow rates."
I must of misread this one from your previous post. I took it to mean that
You thought that if the Springs were too soft and the
pistons topped out too soon, that this would make the mixture too rich
at higher flow rates.
This was the whole reason I got involved in this discussion to set the
record straight on that thought.
(Kids could be reading this) Now You have "No argument " over Softer Springs
= Leaner Running.
Bottom line is the Needles are the heart of tuning the SU's the Springs will
have the least effect.
As Joe Curto says, "most times You can throw through 3 sets of Needles
before getting it right".
We're getting somewhere now.
Sent: Tuesday, December 01, 2009 1:00 PM
Subject: Re: [TR] zenith or su's ?
>> An Increased Spring Rate will make any specific Needle run
>> richer across the whole spectrum. No Exceptions!
> No argument. However:
>> You don't want to compensate for bad Needles with Springs.
>> ...Sort the Car out on the road using the Volvo Needle
>> then see where you are rich...
>> The Springs should be your last concern.
> At no point was I saying one should compensate for anything by swapping
> springs. Let me try this again.
> 1. If the springs are incorrect but you are not aware that different
> springs are even available, you may be tempted to change to thinner
> needles (or bigger jets?) and/or tweak the idle mixture to get it to run
> well on the highway. You will be changing needles and mixture to
> compensate for the springs, not the other way around.
> 2. There is a behavioral change between the piston operating in its range
> and topped out. Once it is topped out the mixture will get richer as the
> airflow increases, regardless of how well or poorly it was set before. If
> you use full-throttle behavior as a data point you will be mislead by that
> 3. It happens in real life that people make that error, swapping carbs
> between engines of different sizes. My GT6 had red (IIRC) needles but
> needed yellow. It took me a long time to learn this lesson.
> Jim M
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