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MG MGB Technical - Adjustment of plastic carb floats.

I am rebuilding a set of HS4 carbs for a 1800 3 main engine. The floats are plastic and there is no way to adjust the float level. One float hangs down more than the other. Using drills to measure the clearance between the float and the float bowl lid, one carb is .041" and the other is .073". Do I put shims under the float needle to make both carbs the same? Thanks for your help and have a good day!

John
John Progess

Yes, you put shims under the float needle body, and then screw it into the lid. You are looking for about 3/16 clearance between the lid and the float, when it is upside down resting on the needle boss.

warmly,
dave
Dave Braun

John,

The idea is to bend delicately float arm to have proper clearance.

Cheers,

Jean G.

P.S. Spacers are used only with groose jets as it is the only way to modify fuel level
Jean Guy Catford

John
Emphasise "bend delicately"- You keep thinking the float will crack any minute! I also replaced the needles with the ones with viton tips.
Having got the gaps about the same (using the appropriate drill bit), I then checked that the two floats were shutting off at the same level by inverting the lids and immersing the float into a small jar with water in it. With some tubing attached, I blew into the inlet and when the shut off occurred at the same water levels I knew the floats were set about right.


John
John Minchin

I am looking at the floats and there is no arm to bend gently. I have a spare plastic float and it has a metal arm but these floats have no arm. The float has a boss cast in the top with a hole for the attachment rod and the boss is what contacts the needle. I would need to add over 1/8" in shims to get to 3/16" clearance and I don't think there are much more threads in the needle body. This is a very poor arrangement indeed! All the other floats I have are very simple to adjust.

John
John Progess

Sorry John,

The only floats I saw had metal arm on them for HS4. I checked in Haynes and they said exactly what I mentioned in earlier post.
"
They say clearance should be: 1/8"(3,18mm) diameter bar paced under the lever and across machined lip, parallel to the float hinge pin.

Have a look there:

http://www.mgexperience.net/article/su-tune.html

Cheers,

Jean G.
Jean Guy Catford

Those are horrible late floats, generally found as replacement parts. For a time that was all you could get, but I believe there are now new production metal arm ones. Try Joe Curto.
There is enough leverage ratio that you should not need anywhere near 1/8" of shims to get it right. Me4asure with spacers between the needle valve and the float at the point of contact.

FRM
FR Millmore

Hi John,

The all plastic floats can't be adjusted, BUT the fuel level can, after all that is what you really want. To adjust the fuel level you will need some special washers that go under the needle seat.
The correct fuel level, according to SU, is 3/8" below the bridge, very hard to do. How I do it is to fully pull out the choke, disconnect a wire from the coil, remove the dome, spring and piston from the carbys and turn on the ignition. The fuel should just be below the end of the jet. I have found that the space between the float and the edge of the lid is 7/16", on both my MGB and my Wolseley, using this method.

Herb
Herb Adler

This thread was discussed between 12/03/2012 and 14/03/2012

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