Modified SU carb needles for L28

[jitenshakun]

SUs don't have a function like an accelerator pump on a Weber, which is one of the reason Webers have a slight edge on immediate acceleration.

The spring and oil are about damping the piston to keep the engine a bit smoother instead of always micro fluctuating with engine speed changes. Spring and oil work together to set how much it takes to get going and at what rate it goes once it is going, respectively.

[Captain Obvious]

In addition to smoothing out variations in piston position. the damper prevents the piston from rising too quickly under acceleration conditions. The delay in the piston rise temporarily richens up the mixture just like an accelerator pump would. So the accelerator pump function may not be direct like the Weber's pump, but the intent is the same. There's a brief note about the function on page EF-19 of the 72 manual. There's probably other (maybe better or more detailed?) in other years FSM's, but that's the one I put my finger on first.

And to answer your original question about the springs... The springs would affect the mixture under all conditions, not just acceleration. The thickness of the damper oil would only have an effect upon increased engine load, but the springs affect everything.

[240260280]

CO is spot on.,,, obviously

You can increase spring pressure or simply add weights on the piston top in the dome to also reduce the lift/increase fuel pull as needed.

 

Some thoughts:

• Would SU work best if piston attained max opening at max torque rpm?
• Would SU work best if piston attained max opening at max HP rpm?

Edited December 29, 2020 by 240260280

[jitenshakun]

Is a different needle needed for a 2.8L?

[240260280]

47 minutes ago, jitenshakun said:

Is a different needle needed for a 2.8L?

yes.

[siteunseen]

1 hour ago, 240260280 said:

CO is spot on.,,, obviously 

Captain Apparently.

 

 

[Captain Obvious]

All I picture is Andy Kaufman.    

Edited December 30, 2020 by Captain Obvious

[siteunseen]

Yes!

That guy is still alive.

Ricky Clifton or something like that...

Edited December 30, 2020 by siteunseen