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SU HS-2 Carb Question

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Tullamore

Tullamore

Jedi Warrior
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I know absolutely nothing about these carburators, but on the top cap of my float chamber there is a small hole directly below the where the fuel line attaches. One of my carbs has a small cover over the hole and the other no cover. However both of them are leaking a LOT of gas (only when the engine is running I should add, doesn't matter if it is just the fuel pump running). I took the cover off and didn't see anything gumed up in there.

Why are those holes there and how do I fix my problem?
 
Hello Tullamore,
it sounds as though the carburettors are flooding, the hole you refer to being an overflow. The first thing to check is the float chaamber lids, remove a lid and invert it. You should have a gap between the top of the float and the highest surface of the float lid of between 1\16" and 3\16".
The original needle valve is spring loaded so if you press on the float it will go lower. The dimensions I gave are before the needle valve spring depresses any. The float on a 69 AH is not adjustable for height, but if it is too low, check that there is a washer between the needle valve assembly and the lid. A bit of grit can cause flooding also but unlikely that both would be affected simultaneously. The other factor is if you have a non standard pump and the fuel pressure is too high, anything above 3 p.s.i. is too much.
I hope that helps,

Alec
 
Yes, I agree with Alec...sounds like flooding.

Your shop manual should give you a complete breakdown of the float chamber, float, needles, etc.
If you do not have a manual (you really should have one) here is a page with some useful SU info:

https://www.manchester-minis.cwc.net/technical/sucarbs.htm
 
I am really confused. I agree after looking at it that both carbs are flooding. I don't know what this needle valve you are talking about it. My valve consists of a chamber holding a ball bearing that when pushed up on by the float cuts off the fuel. Also on neither carb is this ball bearing spring loaded.

EDIT:// I guess this is what you would call a grose jet? And I read that these things are known to flood carbs, what can I do to fix it?
 
Hello Tullamore,
yes, obviously non standard, however the basic setting should still be the same. If the top of the float touches the lid when you hold it upside down, then you need to space the grosse jet with a washer or two until you achieve the setting I quoted.
I'm surprised that it doesn't flood with the pump on and the engine not running?. A simple way to judge S.U. fuel level is to remove the dashpot assembly with the piston (Carefully, so as not to bend the needle), switch on the ignition and fuel should be visible just below the level of the jet. Adjust the float setting to get that level.
Good luck,
Alec
 
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