Welcome to our Site for MG, Triumph and Austin-Healey Car Information.


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 MGB Technical - SU HS4 float height

I have just rebuilt my carbs, finishing off my engine rebuild. Bit flummoxed about the carb float height though as I can't make sense of the various instruction in the manuals.
If I was to set as these say at 3.18mm then I would have to heavily distort the floats.
Now starting to wonder if the floats are the right ones or do you press down against the spring in the valve to measure?
The picture shows the large gap of around 12mm I have at present.
Any suggestions, wrong floats or I am just being particularly thick?


Mate, I think that is the wrong float for a springy needle/seat
The solid steel needle has the float you have there but the springy needle has a one piece nylon float without the metan piece Also I think--?? -not sure though, that the top caps are different for each type
William Revit

Found this ,might help ????


William Revit

Float height is measured with the spring loaded plunger uncompressed.
Have you got a sealing washer bewteen valve body and float lid? Having one fitted lowers the float substantially.
Paul Walbran

Those are the earlier design of float, now superseded by the solid plastic, non adjustable type. The float chamber top looks of the correct design. The clearance should be 1/8" to 3/16" under it's own weight, not depressed. If you can't get that it suggests the needle valve is incorrect or has been installed with an aluminium washer. My parts list doesn't show a sealing washer.
Allan Reeling

Allan, I agree. to clarify my comment about lowering the float, I mean when installed in the carb. In the upside-down measuring mode it does of course make the float sit higher above the lid.
And no, there shouldn't be a washer. My SU catalogue doesn't show one either. Furthermore, without it, with a new float and new valve the height is virtually always correct.
Paul Walbran

There is a fibre washer at the moment, it was fitted to the chamber as I found it.
I'll try removing it and see what happens

This thread was discussed between 18/07/2016 and 19/07/2016

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now