AuthorTopic: what does the dash pot do?  (Read 3016 times)

0 Members and 1 Guest are viewing this topic.

anaxemurderer

  • Guest
what does the dash pot do?
« on: May 25, 2007, 22:34:54 »
What exactly does the dash pot do on my su carbs? As i understand it operates as a damper for the needle. Why did unscrewing the dash pot top whiles the engine was running lower the revs and subsequently upset running? Topping up dash pot and unscrewing whilst engine stopped has sorted it but i am curious!

Nick
3.5 V8 bobtail rrc

Offline thermidorthelobster

  • Posts: 3557
  • Attack: 100
    Defense: 100
    Attack Member
  • Karma: +1/-0
  • Referrals: 0
what does the dash pot do?
« Reply #1 on: May 26, 2007, 09:16:17 »
IIRC when you unscrew and withdraw the plastic cap it pulls the whole piston assembly upwards and hence pulls the needle right open.  So it'll overfuel like mad.
David French
Tree-hugging communist
1999 Discovery II TD5 Manual
Patriot roof rack, QT Services diff guards front & rear, DiscoParts steering guard[/url], Autologic ECU upgrade, 2" Old Man Emu lift, 235/85R16 BF Goodrich All Terrains, Safari snorkel, DiscoParts jackable sills, Warn Tabor 9000

Ex Disco 200TDI, P38a 4.6HSE and 101FC 6x6 Camper.  Africa Trip Blog

Offline Rossko

  • Posts: 297
  • Attack: 100
    Defense: 100
    Attack Member
  • Karma: +0/-0
  • Referrals: 0
what does the dash pot do?
« Reply #2 on: May 26, 2007, 15:24:49 »
The damping also produces a accelerator pump effect. Other carbs have a physical pump to add a dollop of extra fuel when you floor the pedal. SU & Stromberg have the dashpot to slow down the piston movement and give an equivalent temporary fuel richening. Elegant solution :)

cheers, Ross K
GLASS

Offline greasemonkey

  • Posts: 37
  • Attack: 100
    Defense: 100
    Attack Member
  • Karma: +0/-0
  • Referrals: 0
what does the dash pot do?
« Reply #3 on: May 26, 2007, 18:25:51 »
You just need to keep the oil topped up otherwise they do stop working right though
Cheers
Steve
Don't blame me i only work on them
....................................................
visit me @ www.fronteratech.com
Taking part in the Mac 4X4 Challenge 2008
'Team Frontera' Car 23 Sponsor us now
www.justgiving.com/team-frontera
Raising funds for 'Macmillan Cancer Support'

anaxemurderer

  • Guest
what does the dash pot do?
« Reply #4 on: May 26, 2007, 19:52:31 »
Yeah thats roughly what i thought and makes a lot of sense when i think about the symptoms. They don't normally cause problems it was just because they were unscrewed whilst it was running, must have displaced some oil.

Cheers

Nick

Offline Range Rover Blues

  • Moderator
  • ***
  • Posts: 15218
  • Attack: 100
    Defense: 100
    Attack Member
  • Karma: +3/-0
    • South Yorkshire
  • Referrals: 0
what does the dash pot do?
« Reply #5 on: June 01, 2007, 01:21:40 »
Apparently SUs should have very little oil in them, they work ok with almost none, they work great when full, but half full they run rough :?

Used to tinker with A series a lot when I was younger.

And yes, basically the damper (or damper rate) controls fuel enrichment during throttle opening (transience) to prevent missfiring as you clout the loud pedal.
Blue,  1988  Range Rover 3.5 EFi with plenty of toys bolted on
Chuggaboom, 1995 Range Rover Classic
1995 Range Rover Classic Vogue LSE with 5 big sticks of Blackpool rock under the bonnet.

Offline Rossko

  • Posts: 297
  • Attack: 100
    Defense: 100
    Attack Member
  • Karma: +0/-0
  • Referrals: 0
what does the dash pot do?
« Reply #6 on: June 01, 2007, 23:39:15 »
Quote from: "Range Rover Blues"
Used to tinker with A series a lot when I was younger.


Y'know I almost mentioned the old "tuning" tweak of putting in thicker oil for more accel pump on A series!!  I think the advice is not to do that on V8 though, you shouldn't want to if the original design was right.

Someone knowledgable will remind us of the correct oil for V8 SU & Strombergs in a bit ...

cheers, Ross K
GLASS

Offline DEANO3528

  • Posts: 427
  • Attack: 100
    Defense: 100
    Attack Member
  • Karma: +0/-0
  • Referrals: 0
what does the dash pot do?
« Reply #7 on: June 03, 2007, 00:19:54 »
Over the years I think I've heard most of them, from 3 in 1 through straight 30 and ATF to 90 weight!
Truth is, they are supposed to run 20/50 engine oil and they run well on it.
You'll soon know when the oil level is dropping in the dashpots because the motor starts spitting back when you floor it as the resistance to the vacuum lowers.
Cheers
DEANO


anaxemurderer

  • Guest
what does the dash pot do?
« Reply #8 on: June 04, 2007, 16:54:53 »
Always thought they wnated thinner oil than 20/50, will know for the future though. She is back to running very nice now!

Nick

Offline Range Rover Blues

  • Moderator
  • ***
  • Posts: 15218
  • Attack: 100
    Defense: 100
    Attack Member
  • Karma: +3/-0
    • South Yorkshire
  • Referrals: 0
what does the dash pot do?
« Reply #9 on: June 08, 2007, 20:40:29 »
SUs run fine on whatever the engine drinks, stroms are fussy and I know of a couple of applications where a thinner monograde was preferable.
Blue,  1988  Range Rover 3.5 EFi with plenty of toys bolted on
Chuggaboom, 1995 Range Rover Classic
1995 Range Rover Classic Vogue LSE with 5 big sticks of Blackpool rock under the bonnet.

 






SimplePortal 2.3.5 © 2008-2012, SimplePortal