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MG MGA - Carburetor Lever Holes

I found that this came up back in 2002 with no real answer.
I am rebuilding my carbs and got new levers. The holes in the levers for the pins that connect to the link are about .30" but the link pin is only about .18". This leaves a lot of slack in this pivot point. Why is that? Does it really matter?


Steven B

Steven,

On twin SU installations the rear carburetter throttle should open before the front carburetter. There should be a slight delay before the front throttle opens. This is shown in SU overhaul manuals.
I have scanned a couple of diagrams and put them on :

http://www.angelfire.com/amiga/mga/index.html


Mick
Mick Anderson

Hi Steven. My understanding is that this "slop" is necessary in order for the chokes to work correctly, but I cant give a definitive answer as to why this is. Some people try to install bushings to take up the slop, but doing this can apparently cause the chokes to work incorrectly. Cheers, Glenn
Glenn

Glenn is correct. The large holes at the anchor pivot (off the carb body) are essential to the operation of the choke/fast idle sequence.

Mick:
The diagram of the HS carbs is not showing a delay between carbs. This is the setting to give a bit of clearance so that the idle speed is set by the idle screws, and not the accelerator linkage/cable.

The diagram of the H carbs does show the delay between carbs setup, but this only happens on a few cars, mostly if not entirely, sedans - Magnette, Rover, Jag, etc. I don't think any MGA had it, certainly most do not. I never quite got the point or function - it appears to be to do with smooth pickup on heavy cars. I have frequently removed this stuff (commonly worn and/or missing bits, like the roller bushings on the Rover versions) and reverted to the standard fixed and synchronized coupling, which most cars came with. The results always seemed better, though that may be because I always did the change in conjunction with a thorough carb set-up.

Last, going to your third article on the modified dampers: the mod described is not always favorable - Yesterday I cured a very annoying stumble on a B by reversing the mod. Went from AUC8114 back to AUC8103. The car was a 79 converted to twin SU HS4; I could also cure the stumble by making it a couple of flats richer than it really needed, at the cost of excessive fuel consumption - it only needed to be richer on acceleration.
FRM
FR Millmore

Hi FRM,

The mga twin cam H6 carburetters do have the "small pin in a large hole" throtle shaft connection system.
In my Twin Cam Workshop Manual it says to fit the pin in the center of the hole (not at one edge as in SU publications). It does not give a reason, but I believe it is so you can make small idle changes on one carburetter without loosening the front/rear connecting clamp.
I agree with you that it does not seem to have a function in the SU's operating. It is strange that SU factory publications talk of the so-called "delay".

Mick

Mick Anderson

Ya, is strange all around! Didn't know about the Twincam. So you invariably start off with the carbs out of synch, and they stay that way all the way up. Or else you have it idling on one carb and they catch up later - never made sense to me
Some things, Rovers maybe, have the pin with a roller in a cam slot; it's possible that the cam makes the second carb match the first after a while, but I never bothered to figure it out or measure it - It's just too strange.
FRM
FR Millmore

The slop allows you get two actions out of the one cable - first action while you take up the slop is to up the idle speed (first 1/2" movement of the choke knob)- this can be further refined by where you set the linkage arm on the cam (more or less travel). Once the slope is taken up then you start moving the main jets (richens the mixture)- by careful adjustment of the joining link between the levers you can get both to richen the same amount.
I found by setting these up as per the manual my car starts so easily when cold - but then again I am in sunny Melbourne.
Regards
Mike
Mike Ellsmore

Hi Mike,

I suppose it depends on what levers are being discussed. The choke levers or the lever/clamp that joins the front and rear throttle shafts. I am not sure which items Steven is describing.

Mick
Mick Anderson

Mick -
I was refering to the long levers between the carbs, not the joining link. Mike's explanation, along with the others, makes sense now that I think about it.
Thanks to all!
Tomorrow is tranny inpsection, tear down and rebuild day! Woo hoo!
Steven B

This thread was discussed on 24/04/2007

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