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HS4 SU carb float level


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Still fiddling with my carbs...

So, textbook says an eighth inch drill should just fit under the float when it is held upside down and resting on the valve but not with the needle fully depressed??????

Two photos here: float lid is held upside down and the float is resting, under gravity, on the valve in first pic - but there is a huge gap where the drill is.

Second pic is my finger pushing the float all the way down on the needle valve.

Where should I be measuring - or is it all wrong???

The float is all nylon so there is no adjustment that I can see.




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the su manual  for SU HS  sprung needles  states resting on the sprung plunger not depressing it 

gap to top cover 0.062" to 0.187"  ..."this type  is not adjustable"

 (as its a one piece plastic float) the only adjustment is very thin washers under the valve , and thats a faf.

i had flooding and it was a very small (needs a a magnifyer)  worn groove in the float contact platform, new float solved it, no amount of fettling and twiddling worked  nor did new valves , 


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The problem is the later type of float don't have any means of adjustment. This can become a problem if the spindle hole through the float has a small amount of wear or the pressure from the fuel pump is a tad on the high side, both causing flooding. This is of course presupposes the fuel valve is OK.  The only other way of adjustment is to fit a small washer between the fuel valve and where it screws into the float chamber top.

As I am typing this Pete has beat me too it.


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The other problem you can get, which looks more likely based on the OP's photos, and which I had with my Toledo in 2008, is that some valve assemblies seem to be set wrong and close too early. Because the float is not adjustable, the only fix is to find a correct valve assembly. I didn't know that in 2008 until somewhere in Scotland on the RBRR, when the valve stuck and it coughed to a halt. Even after replacing the float chamber cap with the old one (which I'd fortuitously left on the parcel shelf), the 800 miles driven with excessively lean mixture resulting from the wrong float level... had burnt the exhaust valves to the point where, although we were able to limp it round and home again, there was no compression in the morning.

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