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MG MGA - Mismatched carb float bowl bolt/studs

In my ownership of my 61 Coupe the car has always run rich, especially on the front carb, and tuning has been very difficult. A friend who has expertise in SU carbs has checked my car over and reckons that my issue is quite possibly caused by the front float bowl being about 1 cm higher than the rear float bowl. This would seem to be because of a mis-match in the float bowl holding up studs/bolts -see attached photos. I'd welcome the forum's comments before I take steps to redress the situation and get the float bowls matched in height. Thanks.






Tim Prime

Tim
I’m not an expert by any means, but if I understand correctly what you’re saying, I can’t see why the respective heights of the two carbs makes any significant difference.
The float bowls are filled with fuel under pressure from the fuel pump, and the flow of that fuel is controlled by the float in the bowl. So gravity doesn’t really make any significant difference.
Are you sure your not referring to the respective heights of the two jets? As that would make a difference.
Graham V

On second thoughts, I think what I said was not the whole story, and so very misleading. Apologies.
I didn't think about the fuel moving from the bowl to the jet assembly, as that moves there using gravity. So I guess your friend has a good point. I would think that the two bowls should be identical.

I do hope someone with more knowledge than me will appear soon and confirm

Good luck
Graham V

Thanks Graham. Appreciated. Let's see what other comments come in. Cheers. Tim
Tim Prime

Tim,
The three ‘spacers’ (for want of a better description) in the first photo are wrong and should not be there.
I would remove them (replacing the seals also) and check the float shut off dimension too.
Jet heights in both carbs should be checked and mixtures adjusted also (with the carb linkage slack). The actual floats should be checked for solder seam breakage and filling of fuel which will cock things up also.
You can buy unsinkable floats now, if required.

Regards
Colin
Colin Manley

First picture is a 1600 type assembly.
Second picture is a 1500 type assembly.
See here: http://mgaguru.com/mgtech/carbs/cb111a.htm

Yes they are slightly different height.
Also 1500 and 1600 use different fuel needles.

Do check the numbers on the needles.
1500 originally GS
1600 originally 6

It would be nice if both chamber mounts were the same.
Barney Gaylord

Hi Tim

Hearing what the Guru says I have several spare scrap bodies so should be able to get you a match to rebuild from. Give me a shout.

Cheers.

Paul
Paul Dean

Thanks all. My car is a 1600 so I'll replace the front carb float bowl securing bolt (which seems to relate to 1500s) with the same arrangement as the rear one. I'll also check that I've got the correct sequence of washers, grommets etc on both. The carbs are coming off on Tuesday and so I'll provide an update shortly. It would be nice if this sorts out my timing issues. I know both my needles are No. 6. Thanks for the offer Paul - I'll definitely let you know if I need to take you up on the offer. Thanks. Tim
Tim Prime

Just a brief update. The float chamber mounts are now properly matched and its too early to say whether it has sorted out one carb always being too rich. I'm hoping that it might have but I'll need to take it for a decent run to find out. Thanks to all for your comments & advice. My delay in updating has been due to a puzzling misfire issue but I think this is now sorted by some new plug leads. If it isn't one thing its another with these old cars! All part of the enjoyment.
Tim Prime

This thread was discussed between 20/03/2024 and 23/04/2024

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