MGB & GT Forum

I have twin HS4's and currently tuning them. On one of them the float sits lower than the other. I know to invert it and let it sit under its own weight. Is there a method to adjust them. On earlier types you could adjust them. Doesn't appear to be a way on this type. Below is a google image of the same setup

On this type float, the height is adjusted via shims under the needle seat.

I just finished doing this on my MGB with HS4 SUs.

To adjust the levels, you have to remove the needle valves and fit shims - thin washers - under the valves before screwing them back into the cover. It's a lot of trial and error.

Best way to measure the float level is to turn it upside down and try to pass a 1/8" drill bit between the float and the cover. The float should just touch the bit (see pic). You can add or remove a shim or two until both floats are the same, or as close as you can get. It's important to get them close, final synching and adjusting the carbs is much easier if the fuel levels in the float bowls is the same.

I had saved a bunch of small washers of various thicknesses that came with some "Grose Jets" that I purchased years ago and I used those to shim one of my needle valves. I'm not sure where you'd get shims for this job if you don't already have some - someone else will chime in, I'm sure.



Edited 1 time(s). Last edit at 2017-04-30 10:54 AM by 33EJB.

Thanks for the replys. So by adding these shims i raise the seats up. One of the floats sits at 1/8 which the manual recommends but the other is alot higher. I cant lower that one as there are no shims to remove so guess i need to higher the other. In that case, if both floats are level but sitting higher than what manual says, would that matter too much. When i come to set the jet heights would that balance things out?

Yes.

Just check to make absolutely sure that a washer isn't stuck to the cover or the needle valve - they can be hard to see.

Exact measurement of 1/8" is not that important, as long as both are close to the same. Final adjustment of the jets will compensate for any slight differences.

Hi Chris,

Have a read of these articles.

Herb

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Adding shims under the needle/seat will lower the float level. To raise the float level, remove shims as needed. If removing all the shims still does not raise the float level high enough, then add additional gaskets under the float bowl lid as needed to raise the float level.

FWIW, the level of fuel in the float bowl is not what's important; it's only a means to an end, and the end that you need to achieve is to obtain the proper level of fuel in the jet. The level of fuel in the jet will be the same as the fuel in the float bowl since they are both connected by the spiral-bound jet tube connecting the float bowl to the jet in the main carburetor body.

What's important is that the fuel in the jet is at the proper level. The first step is to set the top of the jet down the generally-accepted figure of 0.060 down from the bridge. Then the fuel level in the jet, with the fuel pump on, should be about an eighth of an inch below the top of the jet. This is commonly checked by removing the dome and piston and "puffing" your breath air down into the top of the jet. By doing so, you'll momentarily push fuel down into the jet, across through the jet tube, and up into the float bowl. The fuel level will then "echo" as the fuel bubbles back up in the jet. What most folks aim for is to puff down into the jet and aim for a float level that allows for the fuel to just bubble up and over the top of the jet after puffing down into it.

Setting the float level in the float bowls is simply a means to this end...

Dick

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You are right - - I should have mentioned adding an extra gasket to the lid in my post. I've never had to do that to raise the float level; I've always been able to just shim the needle & seat to achieve the desired result. But - - I do know that adding gaskets is another way to get there and I have several in my parts supply, just in case I ever need one.

Good luck to the OP.

Update.
I removed and stripped down both floats and lids to check for any hidden shims which i hadnt noticed. None where present. Before dismantling the needles and seats appeared level on both. Only when I added the floats they sat at different heights. I decided to swap the needles around and for some unknown reason the floats now sit level. I took them apart and reinstalled just in case and it all seems ok. I've retuned the carbs and so far so good.