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Triumph Spitfire - help with dual SU carbs

Here's the question: I have a '69 Spitfire MKIII with dual SU carbs. On the rear carb, there is a small machined hole just under where the fuel line attaches to the fuel bowl. There is a small spring plate the partially covers this hole, but there is fuel POURING out of it! Will it cause any problems if I simply plug this hole?

Nick Miller

55 Ford Fairlane
69 Triumph Spitfire
74 VPJ Indy Car
83 Porsche 944
85 Porsche 944
95 Ford Mustang


I suspect your SU carbs are the HS type? (has a hose running from the gas chamber to the carburator?) This is the type on my 68 Spitfire.

The hole is the vent and needs to be kept open other wise the fuel delivery to the engine may suffer. I don't recommend plugging it.

Sounds like a float valve problem. You may have a little debris stopping the float valve from closing.

Sometimes they stick and with use may unstick.

If this doesn't happen, you may want to drop the gas chamber from the top and inspect/clean the float and valve assembly.

Mike Petryschuk
Michael S. Petryschuk

Thanks Mike! I took the "lid" off the fuel bowl and checked it out.. The valve seems to be seating, but they are the same valves and floats that came with the car before I restored it :( I think I am going to go ahead and replace them. Thanks for the info, Nick.

i have always been advised to use copper tubes in these holes, and guide tubes to a safe location incase fuel's are proe to the problem you have now sorted.

This thread was discussed between 10/05/2006 and 30/07/2006

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