Float bowl problem

I have been having intermittent flooding of the carb closest to the firewall in my 3-SU carb set-up. Today, I noticed that the float was sitting on the bottom. I figured that it must have developed a leak so I gently removed it. There were no leaks. Then I noticed that the spindle on which the float travels up and down had been replaced at some point with a threaded rod. I believe that the float has simply been catching on the threads from time to time.
I do not see a part number anywhere for this spindle. Does this spindle come out- or is it part of the bowl casting?..can anyone give me some guidance?

Just looking on eBay at a bowl?……looks like it is screwed into the base …I can’t recall mine being threaded all the way down the rod

They are smooth shaft, only threaded at the top above where the float slides.
The rod is part of the float bowl assy. I’m concerned that the shaft is threaded rod as the thread is British so if they changed the rod, the special nut at the top is also buggered.
E S1 4.2 bowls are all the same part and, I believe, same as E S1 3.8. Some other carbs also the same.
What car is it? I will have NOS and used for many of them.

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I think that the rod is originally cast or pressed into the bowl; I’ve never tried to remove one.

If yours has been threaded it should be possible to replace your piece of threaded rod with one smooth in the middle, threaded at the bottom and top.

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Thanks Greg My car is a '68 2+2 that was retrofitted with triple SU’s. I do not know how to tell the age of the carbs. I have included some pics. i assume that if someone installed this threaded rod that they tapped it in. If this is the case, I am hoping that I can simply unscrew it and have a smooth rod machined with threads at each end.

Very pretty engine bay

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The bowl is stamped AUC2009

Hey Kenn:

It might be best to find a complete, good used AUC2009 float bowl unit. From his post above it sounds like @GregB might be able to help you out with that - it’s worth the ask. Good luck getting this sorted out. :slightly_smiling_face:

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Absolutely…NOS or gently used may be the way to go.

That is the SU number for the expected float bowl from the picture. The threads on the top are 1/4 British, probably BSF, as expected and the rod is either cast in or pressed into the casting. Guessing the threaded rod is not British and so that complicates things and the special nut at the top may be damaged. I have nice used in inventory for $80. I also have new but they are expensive. I wouldn’t bother fixing yours and we have a machine shop. Someone on the forum might have a damaged carb where this is still good but you would need to wait and see if someone responds.

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The rod is threaded at the base

Its difficult to remove, as bi-metallic corrosion sets in, heat is essential, and even then the alloy female threads are usually gnarled

I would take up the generous offers from some listers here to supply a complete used bowl with stud

I have many myself, and quite a few would have that problem

You could shave the shank of the rod in situ with a die grinder and/or file

As long as the float rides up and down smooth should work


Thanks to all for the suggestions…very helpful. I was able to twist it out and grind the threads off. The float slides smoothly now without binding.
Unfortunately, the carb won’t stop flowing. the float valve is working, but fuel continues to leak out the venturi opening.
I read on a recent Facebook page that I may want to consider installing a fuel pressure regulator.

Grinding the threads is going to not let the float move smoothly enough unless they are ground way down. Then they can cock to one side. Fuel pressure regulator is only helpful if pressure is too high and since we assume the other carbs work properly that is unlikely. If you are using stock SU pump, pressure is not the issue.

does not take much for this issue

apart from the float possible still binding, it can be wonky, or leaky

The fork I have found to be somewhat devious if its ever been mucked with, especially stretched where it hinges

Finally, the needle and seat are both prone to wear that is hard to detect, the slightest wear or grain of silt will cause a problem, the whole system gets “silty” as well, the bottom of the float bowl would benefit from regular clean, but no one is that fanatical

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IMHO Worth upgrading to puncture proof floats while you are at it …

Perhaps sleeving a buggered up shaft with Brass Tubing of the appropriate size could provide a easy fix.

Thanks, Tony
If I remove the slide/needle, and turn the key far enough to engage the fuel pump, gasoline shoots straight up in a steady stream about 6" high…I am new to these things, but this seems like a lot of fuel. Could I be chasing the wrong problem?

It sounds like your vents aren’t working properly. Make sure your float bowl vent pipes are clear and functional. The assembly sequence for the vent banjos is fiber “star” washer, banjo, AL washer, nut.


Thanks, Mike
You are correct…the vent line was completely plugged. Also, the slide seat had been damaged at installation to the point that it could not be adjusted. I removed it, and used a fine emery cloth to polish it so that it would slide. The car is running much better…still the occasional backfire through the carbs…a little more tweaking and I might get this car going.


tri carb SU is tricky to get running perfect, others may differ

The most important things I have found (once “faults” are eliminated)

  • verify the Jet moves Up & down (ie spring is functioning).

I then set them ~1.75mm down from bridge using tail of vernier

  • I then verify airflow through each card is the same, using a simple Gunson airflow meter

All screws should be lubed and free

Their is a difference between cold and hot running, but the ASC setting controls that

I tune cold, but it must be tweaked when warm

If Jet Depth and airflow are the same through all 3 carbs, it should run well

look for any fuel leaks in carb throats

The meniscus of the fuel should be visible in the jet well, and if everything is perfect, it will be the same height (about 1/8" below top of jet)

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