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MG MGA - Choke - Am I Missing Something Here?

Chaps, Something struck me as very odd when I rebuilt my carburettors recently. When I stripped the carbs, I noticed that the clevis pin hole in both the jet levers for connecting to the jet link was much bigger (3/8") than the pin itself (3/16"), and bigger than the hole for connecting to the bottom of the jet (again 3/16"). The hole does not appear to have been enlarged by wear, but cast that way. Obviously, this made the lever a very loose fit in the link, and there was a lot of lost motion in the choke mechanism, particularly for the rear carburettor (the choke lever for the front one has a hook that engages in a cross-pin in the jet link, and this acts as a fulcrum as soon as the choke knob is pulled, so no lost motion). This clearly makes it difficult to synchronise the chokes correctly. I looked on the Burlen CD-ROM for the H4 SU carb, and this clearly shows that the clevis hole for the link connection is larger than the clevis hole for the jet connection, yet the clevis pins for both are the same size. So replacement choke levers doesn't seem to be a solution. There is no mention of a separate bush for this, so it seems a very crude and sloppy arrangement for what is otherwise a precision piece of engineering. Is there something missing here? Should this hole be bushed to take up the slack - I have made up a bush for the rear carb, but left the front as it was. Does anyone have experience of this arrangement, and should I do anything about it? Grateful for any views on this. Thanks, Adrian B.
A Bennett

When I rebuilt my carbs years ago, I noticed the slop and thought it was just worn. I brazed the hole closed and redrilled it to fit the pin. Didn't work out at all and had to redrill them oversize. I think the reason for the slop is so you can trip the fast idle without raising the jets but having the holes fit the pins also made it difficult to engage and disengage.
Jeff Schultz

I believe you are asking about two parts, one is in the picture. Yes what you found is normal and should NOT be changed. Are the parts #27 and #44 in the drawing the parts you are asking about?


R J Brown

Hi R J, yes, those are the choke levers I was referring too! So they are meant to be like that. It still seems very odd to me that SU should have produced such a crude engineering solution. If the intention is to give some lost motion to allow the throttles some advancement before the chokes operate, I would have expected to see some sort of cam arrangement, such as in the fast idle link. Incidentally, I have never seen an explanation of the three-position fast-idle link in any of the workshop manuals - nor evidently had the previous owners, since it was set to the hot climate setting when I bought it - it was an ex-California car - with the result that it was a bugger to start since the choke increased the fast idle a lot but didn't move the jets much at all!! The POs had run like that for 14 years!!! As soon as I realised how the fast-idle cam worked and put it to the temperate setting it started easily. The things we learn. Cheers, Adrian B.
A Bennett

This thread was discussed on 18/03/2008

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