[Spridgets] SU Question - Accelerator Pump Question

[Ron Soave]

--- On Mon, 2/23/09, Kirk Hargreaves <khargreaves2 at gmail.com> wrote:
> Someone on the list at one time explained how SU carbs make
> up for the fact
> that they do not have accelerator pumps.

a few weeks ago tinydog's list mate ronsoave drooled:

--- Dean Hedin <dlh2001 at comcast.net> wrote...
...a good explanation. A couple of clarifying points -

> when the butterflys go wide open.   The delayed rise is a
> result of the damper (and
> naturally the viscosity of the oil in the damper).

Also, the resistance to the piston rising is greater than the resistance to the piston falling.

> the engine draws more fuel through the main jet.   

Just to clarify if you're wondering how the needle "not rising" increases the fuel flow, the piston damping increases the velocity of the air across the venturi and the bridge. The rate of fuel flow is directly proportional to the velocity of the air, so you get a richening effect.

I can't tune an SU worth a damn, though. The ones on my race car were set up by Craig Chima and I was told not to touch them. My 1970 Midget has the SUs as they came out of the factory, and my street Bugeye has a Weber!

Ron