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MG MGB Technical - Needle & Seat Conversion

I know this is an old topic, but its Spring and time to ponder repair options for the new year.

Looking through the parts books I again came across the option to change the float bowl needle and seat from the brass w/rubber tip to Grose Jet or something like that utilizes a ball instead of a needle. Catalogs typically include a comment of "better performance" or something.

So, once and for all...

What is the advantage or disadvantage of opening up the floats and replacing the needle/seat with the Grose Jet style?

I just love $10 fixes, but I wonder what I'm fixing. I do not know that there is a problem with the needle/seat presently, as I do not see signs of float sticking or excess gas coming out. Although car does run rich, as I've grown to accept somewhat.

Thanks for any comments.
R.W Anderson

Hi,

I had a lot of trouble with the standard rubber tipped needles, three new sets in fact. Each leaked, to the extent that fuel flowed out of the breather vents. I set up a test bed on the bench using plastic tubing to give a bit of a head. Even with only a foot or two of head the needle valves all leaked quite badly. I converted to Grosse jets and they showed no leakage and the fuel level was kept at the correct level.
Others have had bad experience with the Grosse jets and have advised against them.
Before you rush off to change determine if you have a problem with the standard needles.
The way I did it was to unscrew the tube to the jets from the float chamber (on my HS4 carbys) and with assorted plastic tubing and a T piece I jammed a piece of the tubing into the float bowl ( it provided an adequate seal). This piece of tubing went to the T piece, the other end of the T went to the jet tube. The third leg of the T had a piece of clear plastic tubing on it, which I strapped vertically to the side of the vacuum chamber to hold it up. Turn the ignition on and the fuel level should come to the recommended height. With the engine running there will be a slight fluctuation of this level as you accelerate or back off.

See picture, below.

Herb

Herb Adler

Hi again,

Another thought came to mind just after posting the above, about checking the fuel level.
Remove the vacuum chamber, spring and piston, apply full choke, to move the jet all the way down, and the fuel level should be about 1mm below the top of the jet. Unfortunately seeing the fuel could be quite difficult, try using a light to shine down on the jet, which gives a bit of reflection on the fuel.

SU recommend a fuel level of 3/8" below the bridge of the carby, very hard to determine this level outside the carby.

Another recommendation I came across was 22 to 24 mm below the top lip of the float bowl, which is easier to determine and check, and seems to agree with the 3/8" from SU, as best as I could determine.

If you have a steady fuel level, but it is too high (rich running) try adjusting the float level.
If you have the brass float gently bend the hinge, as per instructions in the manual. If, however, you have the plastic float, then you will need to insert thin washers under the needle valve seat, till the level is correct. I used 4 thou gasket paper to make these washers, when I didn't have any "correct" ones. You might need several thicknesses.

Good luck.

Herb
Herb Adler

When the Groose jets first came out, I bought a set for my SUs and then my Weber DCOE. They worked great. But, the company changed ownership and the quality went way down resulting in the many complaints we see listed today. RAY
rjm RAY

Herb

Have you tried the Viton tipped needles available from Moss USA (373-626). Have never had a problem with them.

FWIW

Larry
49 YT
72 BGT
Lawrence Hallanger

Grose used to be said to be better than the originals, but not any more. I've never had a problem with the originals. Nothing to with performance in terms of HP or torque, a float valve either shuts off as it should or leaks. If it leaks you replace it.
Paul Hunt 2010

This thread was discussed between 26/03/2010 and 27/03/2010

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