Not Starting Problem

[Mike Wattam <MikeWattam@domain.elided>]

Hi Nick

You got the 20 minute rule, a popular complaint!  You were very lucky to
get the repair man to turn up so soon.

Various theories have been expounded on this one, some of them must be
good.

For my money the problem is pressurisation of the fuel system under heat,
causing fuel to dribble out of the jets and down into the manifold. 
The fuel lays in the bottom of the manifold until you try to start, bingo
too rich/fouled plugs!  Wait 20 minutes for the fuel to evaporate, and it
starts fine.

 I have seen only 2 of the many cars which have this problem, and a
characteristic with both was that if you remove the carburrettor adptor
block while this phenomonen is about, there is a puddle of petrol in the
bottom of the inlet manifold.

In one case, the float needles were very worn and with the worn (widened)
seats possibly not seating properly.  Thus fuel under pressure was able to
pass through.  In the other case, the Stag had an electronic fuel pump
fitted.  Fitting the correct SU pump stopped the problem.  Note the MGB SU
pump looks identical but is set to operate at a higher pressure with the SU
carburettors, so should not be fitted to the Stag - I suspect there are
Stags running about with the MGB pump on.

Both the above cars had their float chamber vents malfunctioning.  One was
blocked by debris, the other had been blanked off at the carburettor by
DPO!  Worth checking this drain pipe is clear, first.

Those of you who are actually experiencing this problem - or have cured it
- I would be very grateful to receive your informed comments please. 

IMHO - Mike Wattam
Chairman - Triumph Stag Register