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MG Midget and Sprite Technical - Spring reminder

Since I've used a single HIF44 on my Sprite for 20 years I find my brain has now mislaid the detail of where to connect the carb springs for a twin SU set up.
This is for the frog which has a 1098 engine and twin SU carbs. It should be logical but although I've tried various configurations I'm still not sure which is correct.

So, 2 carbs, three springs,5 possible linkage points....?
GuyW

Hope this is of some help.

R Farrar

Thanks. Smart photos. Unfortunately it obscures the top attachments of the two outer springs. Are they pulling on the butterfly levers, or on the choke levers?

On mine there isn't a very positive return of the choke levers when I push the dashboard knob in (or remove the clothes peg 😂). Perhaps the outer springs should be assisting that?
GuyW

Guy

The springs go on the butterfly levers. The choke should return using the internal spring on the choke lever.
Is the choke cable free? Mine just shuts off without the obligatory clothes peg
Bob Beaumont

Bob, that's how I've been running it. But then wondered if, as the middle spring to the quadrant is effectively also closing the butterflies, should the other two go to the choke levers which don't seem to snap fully down.
GuyW

I think the two outer springs act as a fail safe, to ensure the carbs shut down. Certainly it was a requirement by scrutineers to have a seperate spring for each carb plus the cable. I imagine BMC just continued the practice.
Bob Beaumont

If you can wait for a few hours or until tomorrow morning, if nobody else does first, I'll get pictures of mine Guy.
anamnesis

Here's one I made earlier, back in 2010.

Is this helpful Guy?

I can get a better detailed one later if this doesn't help.

anamnesis

From underneath - does this help Guy?

Bill Bretherton

Yep thanks. That's how I have had them since I re built it. Then yesterday I decided to re-torque head, do the valve clearances, sort out the tappet cover, and then refit the carbs. At which point I had a 'moment', as one does, and thought is this right? Surely the butterflies close when the quadrant spring pulls it round to its stop? And why is there nothing to make sure the choke is properly fully open once its warmed up? Logic you see, is a fearful thing to let loose!
GuyW

The butterfly springs as Bill’s pic also are needed (apart from there normal job of closing) when tuning as each carb is then independent and the third takes up the slop in the cable/ closing both together when re-coupled

Over the years on different SU set up’s I’ve often had to sit and work it out as well.

R.
richard b

If just relied on one spring and you adjusted the quadrant so that it closed the butterflies, there would be a lot of lost movement when opening the throttle.

If you adjusted the throttle levers as per the manual, the butterflies would be able to float around and you wouldn't get a stable tickover. In fact they wouldn't be stable at any engine speed.
Dave O'Neill 2

This thread was discussed on 22/04/2023

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