Hey Bill, Everyone...
It turns out that I was closer to getting my '76 tuned to perfection
than I thought! Seems a silly thing to overlook- dashpot oil levels. I
hope the below explanation from Bill will help to explain that last
nagging symptom that I reported- sputtering and low pep at lower RPMs,
with improvement at higher RPMs.
I mean, as soon as I hit the gas pedal after she was warmed up...I could
tell!
It was a lovely spring day in Vermont- sky so blue it hurt your eyes-
the close and distant hills and dales tinged with that brand new
green-the promise of verdant, cool shady summer to come...
And I was IMMERSED in it...top down, and my old pal running soo strong
and smooth...I mean, the tune coming from under the bonnet and out the
tailpipe was the sweetest music. No need for radio...
Yes, I waxed poetic over this exhilarating experience- the drive through
Vermont's rolling countryside, but also...that with the help of you
great guys on the list...I experienced the satisfaction of bringing her
back to full health.
I don't expect to be pestering you all for awhile...I think I'm just
going to enjoy her for now...at least until that tinkering itch needs
scratching again.
Final word- I am in the tech support business. It is a steady stream of
problems and complaints. I accept this, as it is my job...but every once
in awhile...isn't it GREAT to hear a success story?
Again, my thanks to you all- Bob Lang, Dick Taylor, Bill McIntire, John
Shewmake...and soo many others. This resource is AWESOME!!
Pete
'76 CF51563U, Stylin' and Pro-filin' in Vermont
-----Original Message-----
From: william mcintire [mailto:william.mcintire@wright.edu]
Sent: Friday, May 02, 2003 10:09 AM
To: Kronberg, Peter
Subject: Re: Latest on new Stromberg needle tuning woes
Pete
Yes it is richest when the needle is up. But, and
this is gonna be hard to explain....
The carbs are considered to be expanding choke or
variable venturi carbs. The effective hole for the
air to go through changes with engine demand
(throttle position). At WOT the pistion goes to
the top of its travel and allows as much air as
possible through. If you open the throttle at
relatively low rpms and there is no damping
(oil/spring) to retard the piston's movement it
will be pulled to the top of it's travel very
quickly. The fuel in the jet is at atmospheric
pressure (+/-) and relies on the relative lower
pressure of the air moving through the carb to
sorta suck the fuel out. So if you nail it say
around 2k rpms the undamped piston will go to the
top and provide the air the engine wants. So the
engine has the air but the velocity of the air
though the carb is relatively low as the engines
real need for max air isn't reached until high
rpms. The vacuum created throught the carbs is
low, or closer to atmospheric pressure of the fuel
in the jets, so not as much fuel is sucked out.
This creates a lean condition until the engines
real need for air brings the velocity of the air
through the carbs to a point where there is a
sufficient pressure differential with the fuel to
create the proper mixture. When you open the
throttle the piston doesn't respond immediately.
This creates high velocity air through a small
opening with a resultant pressure drop so more
fuel is drawn in to help initial acceleration.
HTH
Bill
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