ausmini
https://www.ausmini.com/forums/

SU dashpot springs
https://www.ausmini.com/forums/viewtopic.php?f=2&t=13533		 Page 1 of 1
Author:  J_A_M [ Mon Nov 28, 2005 9:41 am ]
Post subject:  SU dashpot springs
I have these dashpot springs:

Image

But I also note you can get these:

Image

My carbs had one of each when I pulled them down for rebuild :shock:

How does each effect the performance of the carb (and dashpot piston) ?
Author:  poeee [ Mon Nov 28, 2005 10:32 am ]
Post subject: 
They can effect performance as much as the wrong needles.

What do you have in there now?
Author:  Matt68 [ Mon Nov 28, 2005 10:39 am ]
Post subject: 
different strength spring to adjust how much throttle is required to raise the dashpot fully. If you have the wrong ones then your dashpots will either raise too quickly and be fully open at too low revs, or be partly closed at top revs.

Use two blue ones for an 1100 or 998 ( it think)
Two red ones for a 1275.

This is for twin HS2s

Cheers
Matt
Author:  drmini in aust [ Mon Nov 28, 2005 10:41 am ]
Post subject: 
Vizard suggests Red ones mostly, for a 1098 with twin HS2s.
see p86 of his yellow book.
Author:  Matt68 [ Mon Nov 28, 2005 10:42 am ]
Post subject: 
Thanks doc,

My memory was a bit dim, I've only dealt with 998s and 1275s so far!

Matt
Author:  J_A_M [ Mon Nov 28, 2005 10:47 am ]
Post subject: 
red, blue, purple.....no old ones still have the colour on them.

How can you VISIBLY tell the difference??

I have these:

Image

*********************************
EDIT: nevermind....MiniMania say that one above is a RED spring. That's what I am using then :wink:

http://www.minimania.com/web/TextSearch ... entory.cfm
*********************************
Author:  miniron [ Mon Nov 28, 2005 10:53 am ]
Post subject: 
:?

JAM,
The dashpot springs are there for one and only one reason. They are to prevent the piston reaching full lift before the engine reaches full RPM.
If the piston reaches full lift before the engine reaches full RPM then the mixture will not be adjusted correctly for increasing RPM. ie the needle cant rise any further.
The springs tend to fatigue and lose their strength over time so should be tested and replaced regularly when necessary.
There are several springs with different rates.
The general rule of thumb is large engine-small carb=stronger spring, small engine-large carb=weaker spring.
It would seem that whoever replaced the springs in the past didn't or couldn't get 2 springs the same. They are colour coded on one end and it doesn't take much for the colour to disappear. Twin SU carbs should have both springs the same. For Cooper 'S' and Clubman GT with 1 1/4" SU's they should be RED.
The strength of the different springs varies from 2 1/2 oz to 12 oz at the test length.
RED should be 4 1/2 oz at a test length of 2 5/8". To check borrow the kitchen scales and get a piece of tube that the spring will fit inside and cut to the test length of 2 5/8". Put spring in tube and place on scales. press down on spring until it is compressed to length of tube and read scale. This is strength of spring at test length.
The damper controls the rate at which the piston rises as engine speed and vacuum changes. (It doesn't do anything when vacuum drops and allows the piston to fall immediately) This is the "SU accelerator pump" to give a richer mixture during acceleration. It depends on the oil in the damper to control the action. This is why you get a flat spot on acceleration if you don't keep the oil topped up.

Edit: In the dim dark past SU pistons came in different weights and most/all? didn't have springs. Hell of a lot cheaper to have one piston and a selection of different springs to achieve the same result.

Hope this helps
RonR
Author:  benjamin [ Mon Nov 28, 2005 11:06 am ]
Post subject: 
drmini in aust wrote:
Vizard suggests Red ones mostly, for a 1098 with twin HS2s.
see p86 of his yellow book.


pg92 in mine but there is no metion of 1x 1 3/4su :(
Page 1 of 1 All times are UTC + 10 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/