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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Carb throttle openings (different thread!)

engineyone point me to a good article anywhere, or explain personally, why the throttles on the H6
B Mayo

Answer no, but never heard of a set up other than a synchronised one. But then again never worked on a Twin Cam!!
Allan Reeling

They are called front and rear coupler levers. I think the hole is supposed to be round, not slotted, and not a lot of clearance. The Workshop Manual says to be sure the pin is centered in the hole when at rest, but I don't think it should have much free play, meaning no intentional delay in opening the second throttle plate.

Idle speed should be synchronized before the coupler is centered and tightened on the shafts. I think it is only to assure that the front and rear carbs are not fighting each other when it comes to making very minor adjustment to idle speed when you would be turning one idle screw at a time (and only a small amount for each one).
barneymg

Bruce, MG Z Magnettes had the same arrangement. As I recall ( I no longer have the workshop manual) the delay to two carbs opening together was to give a less jerky take up on the initial throttle pedal movement. I adjusted mine so that the carbs were synchronized once the delay was taken up, i.e. above tickover.
Lindsay Sampford

Here you go Bruce, just found it on line. See the image. If this is the device you are talking about the adjustment instructions may help.
Lindsay.

Lindsay Sampford

Thanks Barney but I do recall some time in the distant past that there was a definite reason for a bit of “slackness” in the linkage to allow one carb to open a bit before the other. I think Lindsay might have found the relevant wording and a similar looking diagram from the Magnette manual. Not sure that any of it makes much difference actually, but interesting history!
Bruce.
B Mayo

Bruce,

I would suggest that you try having a clearance between the pin and the slot on your mga twin cam.
Looking up my SU Overhaul Manual it says that there should be 0.006" clearance. My Triumph Workshop Manual says a 0.010" clearance.
I have always used the clearance on the MGA Twin Cam and my Triumph cars. I am not sure why it is used. Maybe for very fine idle adjustment or smoother take off. Either way the manufacturers seem to think it is important.
Some SU's have a round hole but the MGA Twin Cam has a slotted hole.

Mick
M F Anderson

Bruce,

Do you have a slot or a round hole in that coupling?
I have seen both types. The MGA Twin Cam Service Parts List indicates a round hole but you say you have a slot.
The SU Overhaul Manual shows a slot.

Mick
M F Anderson

Bruce,

The MGA Twin Cam Workshop Manual states that you are to "make certain" that the coupling pin fits loosely in the centre of the hole. (See attached image).
I suggest you try it as who are we to question the factory's (obscure) reason

Mick

M F Anderson

Similar comments in the Triumph Workshop Manual, but this time with a slot rather than a hole.
(See attached image).

Mick

M F Anderson

And again in the SU Manual, also with a slot.
See attached image.

Mick

M F Anderson

Mick
Thanks for all that. I did quote a slot rather than a hole but that was from memory. Need to check and confirm - away from home for a couple of days but will look then. As you say, an obscure MG instruction indeed from back in the day. .006 or .010 - all very precise!
Bruce.
B Mayo

This thread was discussed between 29/11/2017 and 30/11/2017

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.