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MG Midget and Sprite Technical - Carb Qs

Pursuant to previous mail stamped on my carb body on inner face of throat is AUC 6020. These thus appear to be a H4 of some description - as used on MGA amongst others....see pic with original carb shown

They look and operate well enough when engine is warm, but I am a little concerned about the choke linkage (the brass arms) under the carb bodies.

It is shown as it came off the car - car is new to me so not my fault guv. It doesn't look particulary great, although it does work somewhat - the main thing is that it seems to pull both jets down by a sort of equal amount. Tinkering required though...

However, there is no linkage from this choke linkage to the throttle - no fast idle cam or mechanism as per the OE carbs

I have trawled Google a little, and so

1 Did these carbs have a link to the throttle originally? Some pics on interweb thingy appear not to have this link. If so fine, I guess they may run OK on choke without it if properly set up

2 If needing a link to throttle, How to retrofit a link?

Mark O

Some creative engineering there.
The brass arm on the LH carb is MGTD or Triumph or something, not MGA. The other one looks homemade. Two missing springs and some clevis pins. And the link to the fast idle cam. The steel channel links go in the big boles in the arms; if there are no big holes some idiot has filled them.

Looks like you have two RH or rear carb bodies, which probably means these started as Morris or some single carb set. The ID tags are pretty useless, as they can be swapped or lost easily. Are the two float bowls vertical when the carbs are mounted, or at least at the same angle?

Fast idle cam goes on a threaded boss on the side of one carb, just outboard of the throttle shafts. One throttle stop/idle screw should have a second screw to engage the fast idle cam. All carbs have the boss, though it may not be threaded for the shoulder screw the cam pivots on.
You can live without the fast idle, but then you have to play with the pedal when cold, which most people cannot do correctly.

Numbers are not "stamped"- there are "cast in" numbers which are the casting, and "electropencil etched" numbers which tell you what the casting was machined for. Electropencil numbers are frequently hard to see, especially if somebody has beadblasted or otherwise disturbed the metal surface. This is not just pedantic, it matters, as does the distinction between "casting", "forging", "stamped in" etc.

Give me some more pics from different directions and I can tell you more. And look on mgaguru.com for how they are on MGA. Parts can be swapped around in almost infinite combinations, several of which may work.

FRM
FR Millmore

Agreed FRM...I too am rapidly coming to the the coclusion that the choke linkage is at the very least bogde job from a number of different car part bins!

The cast numbers - apologies - state ACU 6020 - so nor reason to doubt that they are H4s anyways. Guess the ideal solution is simply to buy the correct bits from MGOC or similar - but £££££!

I think I may have a go at robbing the fast idle cam/screws and any linkages from the OE carbs, and retrofit to these - somehow - to the choke linkage and threaded boss you mention. As long as it open the throttle butterfly valve and can be adjusted - then that basically fulfils the requirement.


Good point about carb bodies - will check that out.

Cheers

Mark
Mark O

Mark,
from FRM's comment that the carbs might not be twins and to introduce you to John Twist videos - this video shows matching pistons -
http://www.youtube.com/user/Universitymotorsltd#p/u/134/IfU47Oqq9wA

and these might give you a different view to much of what you already know about SUs -
how a SU works part one
http://www.youtube.com/user/Universitymotorsltd#p/u/131/7GRAcqDySog

how a SU works part two
http://www.youtube.com/user/Universitymotorsltd#p/u/132/60Bj_2cZQnc

I've got some old carbs my mate gave me as I needed one set screw from them so if you need any parts from them they're yours for putting a donation in the collection jar at your local pub but sorry no linkage bars

Nigel Atkins

Understood - I will try some creative engineering of my own to link open the throttle on choke.

I will have a go to balance the two, set the mixture correctly, adjust throttle stops, build in some sort of link and see how it goes. They are basically just a venturi after all...
Mark O

don't forget the matching pistons before you start as this could save you a lot of time and hassle -
this link might be more direct - http://www.youtube.com/watch?v=IfU47Oqq9wA&lr=1
Nigel Atkins

Just watched it - I like it Nigel, the man is a star!
Mark O

a couple of hundred videos remain up, one even shows a fail, most are really good and of interest and all charmingly lacking in slickness :)
Nigel Atkins

Mark-
HS parts are totally different = useless.
Any single H4 or one of a pair should have the fast idle cam, bolt, & link, but you need to have the extended double screw throttle stop lever - where's my pics?

FRM
FR Millmore

Mark,
FRM will be able to help you greatly with the photos up

as I was looking for John Twist videos I found this one that might help withother things to check/look for and give you more background info - http://www.youtube.com/watch?v=GHNlT5yHDxk&feature=plcp
Nigel Atkins

This thread was discussed between 16/08/2012 and 17/08/2012

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