I know that needle profile seems to have a lot to do with when you are
as much as where you are.
I've been told that cars running in high altitudes run better with a
different needle than stock due to changes in air density. This also
seems to be the case with changes in fuel composition or octane levels
over the years.
When I bought my roadster in the 70s, it ran super on stock needles,
even ingesting 89 octane regular. Then I got married and put the toys
away. About 20 years later I decided to rebuild the car and found that I
could not get a decent idle and/or smooth revving above 4000. After
changing to a non-stock needle profile, things went back to running nice
Then the front carb would not stop leaking gas, so I got a rebuilt set
from Z Therapy. Until I swapped the needles to the non-stock profile I
used in my old setup, I had similar idle/revving issues. She runs better
than super now. Go figure.
By the way, I live in California. What's a 'choke'?
To: RacerY@comcast.net, email@example.com
Subject: Re: [Roadsters] su chokes are backwards- they're 'enrichers'
Date: Wed, 03 Nov 2010 11:27:05 -0400
I had heard that if the car starts without the choke then the mixture is a
little rich. Perhaps that is more true with the stock needles. Also seems
easier in the summer than winter to start without the choke.
From: Toby B <RacerY@comcast.net>
Sent: Wed, Nov 3, 2010 12:05 am
Subject: [Roadsters] su chokes are backwards- they're 'enrichers' not
"That's back wards.
You pull the choke to start your engine. When you pull the choke, it
the air flow into the carburetor thereby enriching the fuel mixture. You need
to enrich the mixture when the engine is cold."
Actually, on an SU, the main jet is lowered, adding more fuel to the mixture.
Additionally, the throttle plate's pulled open a bit to add air. No
'strangler' for an SU, just a 'gasser'.
And thus, if your mixture is too lean, your jet set too low, your
float level's low or crud's built up on the inside of the jet body,
the car will only run 'on the choke' which is really 'on the enrichment
Weber DCOE's have an entire little carburettor to do what an SU does by
the main jet a few mm.
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