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spitfire carbs


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 Spitfire SU HS4 carb problems (FZX1122) SOS


I have trouble with my carbs and need some advice.

Having difficulties setting up the carbs I decided to have them rebuilt by a specialist company.

They were fitted with new AUD 9450 jets and ABT needles ( ex rimmers). They were delivered and fitted by the company and setup. They ran perfectly and I was delighted until a few days later I started the car and they ran very rough due to a rich mixture in all four cylinders and it would not tick over. I called out the company and they came out and set them up again to run perfectly. Again a few days later I started the car up only to find that it ran as rich as before.

I have checked that the fuel is flowing freely, the floats are working properly and do shut off the fuel supply, the float chamber overflow pipes are clear and dry, the jets go down and up and the needles go up and down as they should and the crankcase vents is clear. The air filters and gaskets are on the right way and the flexible fuel lines have been replaced recently (within the last 50 miles)

I am now at a loss as to what to do next. I am always coming back to the fact when they are set up they are OK but a few days later they are not.

Has anybody had this or a similar problem? I would appreciate any suggestions.







there is no reason why they should go out of tune ,, the question is what  did they do to make it OK


thats the clue  ...do you know what happened ????


this has all the signs of the choke is not returning , apart from fuel  levels and float needle problems there is nothing else to make it 'rich'  


youve checked all the normals  so now its a guessing game .



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Sounds a little unusual.  Going weak is more common, usually due to air leaks elsewhere but not going rich.


Couple of obvious things to check:

  1. Are the chokes returning correctly/fully?  Once you've pushed the choke all the way in from the cockpit check that they are fully up in the engine bay.  Should just see the bottom of the carb then the solid bit the flexible fuel feed from the float chamber connects to.  If there's any gap/you can see the metal pipe that comes out the top of this bit they haven't returned home so although the button's in on the dash the chose is still out.
  2. There ARE a springs around the mixture adjustment nuts?  If these had been missed in the rebuild (and not spotted by the tuner either time) engine vibration could be slowly winding them down, richening the mixture.  Unlikely but...
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