Posted By : Chris Taylor, 16-Jun-2005,
06:13pm
The original mechanical fuel pump on Triumph engines regulates its own fuel pressure. The distance the diaphragm is pulled down against the spring by
the camshaft action achieves that. It is the spring pushing the diaphragm back that applies the pressure to the fuel. The only way to increase it (not
that you should need to) is either to increase the stroke of the cam on the camshaft (not exactly achievable except by regrinding the camshaft!!) or
maching the face of the pump so it sits closer to the block. Again not worth doing, although minor adjustments could be made by changing the number or
thickness of the gasket between pump and block.
The traditional British SU electric pump works on a similar principle that the solenoid action draws the diaphragm back against a spring, and it is the
(fixed) tension in the spring that applies pressure to the fuel. Both tend to produce quite low pressures (approx 1 - 2 psi?) which should not cause
float chambers to flood.
HOWEVER, there are other sorts of fuel pump that can produce higher pressures. Larger carbs than standard (like your Weber) also demand a higher fuel
flow, so sometimes a higher pressure pump is fitted so your carb does not run out of fuel at maximum power. In such cases (depending on what you
started with, what you are using, whether the bits all matched or came from different sources) you can end up with a pump that works at a higher
pressure to achieve higher fuel flow, but that higher pressure may overcome the float chamber needle valve and cause the engine to run too rich or even
fuel to folld out of the carb. It is to regulate the fuel pressure such that enough fuel flows but not at too high a pressure to cause flooding that
pressure regulators became popular, often incorporated in a filter (the Filter King for example).
A regulator between an original pump and the carb cannot increase the fuel pressure or flow rate, but neither should you need to reduce it, although by
adjusting that regulator you could probably do so. In effect you do not need a pressure regulator if using an original mechanical or SU type pump. If
it's there though, and seems to be doing no harm, especially if it incorporates a filter, leave it there!
If you have a higher pressure type electric pump (Facet type for example) you MAY need the regulator to ensure the fuel pressure does not cause
flooding. Ideally you want the pressure as low as possible consistent with not getting fuel starvation at maximum power output. If everything runs ok
now, you've probably got that situation so don't meddle!