Float chamber extensions

General Chat with an emphasis on BMC Minis & Other iconic cars of the 1960's. Includes information on MK1 Action days.
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wantafaster1
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Float chamber extensions

Post by wantafaster1 »

Didn't want to hijack the other H4 thread

Can I ask, are the extensions fitted purely for more capacity?
I'm thinking that the fuel level in the main jet must be different, doesn't this affect the running?
Smithmaps
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Re: Float chamber extensions

Post by Smithmaps »

The fuel level must be returned to the original level as required without the extensions.
This is accomplished, either by bending the float arm (which in my view is a bit of a bodge).
I have achieved it by buying foam stay up floats and making longer ones by buying three and cutting one in half.
That way, the tops can be retained as standard. So far this has worked very well indeed, and you don't even need to glue them together, you just chuck the bits in.

Extensions are a bit of a minefield, and over 40 or so years, nobody has been able to give me a suitable explanation for their use.
But used they were.

My personal opinion, is that they were originally fitted to correct the fuel level on the original 20 degree MGA float bowls on a Mini Manifold.
By the time SUs manufactured proper 'Mini' 30 degree bowls, 4814 and 4815, in 1964/5 their use had become so ingrained by all, that they continued to be used, without actual reference to their original purpose.
To my mind, having empty space above the fuel level in the chamber, which is what it amounts too, serves no useful purpose whatsoever, and cars without them seem to function just the same. I know that fitting the smaller floats is also common practice, and will in fact give slightly more fuel capacity, but that is another conversation, and that is also what I have done quite successfully.
But unless you have a race or rally car which you want to re create as period, you really don't really need them with 4814 and 4815 bowls.
mk1
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Re: Float chamber extensions

Post by mk1 »

For years I had a specific problem on long corners that I took at high speeds in my Hillclimber. Chippy's at Harewood was the best example. About 2/3rd's of the way around the corner the car would start missing. After trying a number of "fixes" I eventually came to the conclusion that it was fuel starvation. I was using a pair of H4's with std float chambers.

I replaced these with a set of the Swiftune extensions & the problem immediately went away & never returned.

I never managed to get the float level issue completely resolved, meaning some fuel would dribble out of the jet when the car was stationary, this however was never an issue on a competition car.

I am using the same H4's on my current S, but have removed the extensions as they are not required for more sedate running on the road.
Nevsmini
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Re: Float chamber extensions

Post by Nevsmini »

I’m my mind if you want to run fuel bowl extensions and get the value out of them and keep the fuel level correct you fit the same thickness spacer to the bottom. Then you have more fuel and the correct fuel level.
mk1
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Re: Float chamber extensions

Post by mk1 »

That certainly makes sense.
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