Spitfire SU Carbs

[Triumphgt6]

Finished building the car last year and ran it around last summer. This March had the carbs tuned and ran fine. Now the rear carb keeps overflowing, so bought new float and jet etc but still overflows after about 20 seconds. Adjusted the float as per the manual but still floods. Had the front float out and all looks ok. What next to stop it flooding?

[Steve P]

Have you got a new pump or the original ? most new ones put out too much pressure, up to 6psi when you only need about 1.5 -2 for SU`s.

I believe you can use spacers on the pump mount to relieve the arm a bit giving lower pressure.

If you have new floats and Jets (do you mean float valves?)  try removing the float lid and closing the valve with your finger and see if you can blow air through it, if not it must be too much fuel pressure.

Steve

[dannyb]

Have you a pressure gauge you can test to see if the pump is putting out too much pressure. 

Is the petrol pump recently been changed.

Danny

[Stratton Jimmer]

I had the same problem with the front SU HS6 on my Sixfire. Initially, I padded out the pump with extra gasket adding about 3mm of spacing. Ultimately it was Pete Lewis's favourite "black slivers" of rubber that was causing the problem. Changing all of the fuel line rubber for Gates Barricade (available from the club shop and other sources) resolved the problem completely and the extra gasket is now removed. Since then, I have switched to a pair of Stromberg 150s and back to the SUs for comparison. The Strombergs are superior in every respect!

Edited June 6, 2023 by Stratton Jimmer
Misspelling.