[Spridgets] SU Question - Accelerator Pump Question

[bv]

Kirk,

I've found a few articles that explain it this way: 

"Good acceleration requires a rich mixture, but SUs have no accelerator
pump. To compensate for this, the piston damper slows the piston's rise
when you step on the gas. This temporarily increases air velocity over
the jet and draws more fuel, thus enriching the mixture. The effect is
only temporary, returning to a leaner condition for cruise."

See the two URL's below for reference, and search on 'accelerator pump'.
It is also stated that you can 'increase' the accelerator pump action, by using thicker oils in the su dash pot, to delay 'piston rise'.

http://www.mossmotors.com/forum/forums/thread/11209.aspx

http://books.google.com/books?id=CTz2EAp2ua8C&pg=PA67&lpg=PA67&dq=su+accelerator+pump&source=bl&ots=gs0qmgqIhH&sig=gemAmGKVzLTg0r4jSoQ1KOIAt3w&hl=en&ei=5iukScaPBqCSsQPpxNiwAg&sa=X&oi=book_result&resnum=6&ct=result


Regards,
Bryan Vandiver
59 bugeye
San Jose, CA




--- On Mon, 2/23/09, Robert E. Shlafer <pilotrob at webtv.net> wrote:
From: Robert E. Shlafer <pilotrob at webtv.net>
Subject: Re: [Spridgets] SU Question - Accelerator Pump Question
To: "Bill L" <pythias at pacifier.com>, "Kirk Hargreaves" <khargreaves2 at gmail.com>
Cc: spridgets at autox.team.net
Date: Monday, February 23, 2009, 6:51 PM

Purrfect! :)

Cap'n. Bob      '60 :{)


-----Original Message-----
From: Bill L
Sent: Monday, February 23, 2009 5:05 PM
To: Kirk Hargreaves
Cc: spridgets at autox.team.net
Subject: Re: [Spridgets] SU Question - Accelerator Pump Question

Hello Kirk,

     It has to do with the rate of rise of the piston. ...

     the carbs operate atmospherically. when you press on the pedal, you're
     opening the butterfly valve. This allows the engine to SUCK more. ..the
     There is an air channel that is arranged so that when this suck is
     increased, the piston to which the needle is attached rises, allowing both
     more air, (from the air cleaner) and more gas (because you've pulled
the
     needle out of the jets) to flow. You can't flood the carbs because
they
     only deliver as much air/fuel as the engine will suck...

     no to the point.  the oil in the damper limits the RATE of rise of the
     piston. This limits the amount of air that can flow sucking relatively
more
     gas from the jet, causing an increase in the richness of the mixture
during
     acceleration. When the engine again achieves relative equilibrium the
     distance of the piston out of the jet (and thus the amount of gas flowing)
     and the flow of air are stoichiometrically in balance. (theoretically)

     if this isn't true someone will, i'm sure, correct me. .. PLEASE!

-- 
Best regards,
 Bill L.                           mailto:pythias at pacifier.com
 
 '66 Sprite MKIII HAN8L49403   "the red thing"
 
  Taken as a whole, the universe is absurd 
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