OK, I asked you all to throw away your SU pumps and replace them with a more
reliable unit (perhaps a higher pressure pump and an adjustable pressure
regulator). The resulting discussion has been interesting. There are many
defenders of this pump and they make valid points. You can, it appears, get
improved reliability by making modifications. You can get look-alike
replacements which are purported to be somewhat better.
This is all well and good, but for a car which my family members will drive,
I have decided I want something better. The next generation Ted Bundy or
Jeff Dahmer is waiting to stop to help a stranded motorist somewhere.
But ignoring the question of reliability, is the SU pump really the best
choice when it comes to supplying fuel to SU carbs? The SU carb is notorious
for sensitivity to fuel pressure and dirt. On my cars I use a high pressure
US made electric pump, mounted by the tank. On the firewall near the carbs I
have an adjustable pressure regulator. Before the fuel gets to the regulator
it goes through a decent fuel filter.
With an SU pump mounted down by the tank I see the following problems:
The pressure regulation is built into the pump, which is 2-3 feet below the
level of the carbs. Also the length of the line to the carb is a factor,
what about the effect of acceleration and deceleration on 10 feet of fuel?
With the pump and carbs at opposite ends of the car, the relative position
of them changes going up or down hill, which must affect the psi at the carb.
Istalling a fuel filter between the pump and the carbs will affect the
pressure at the carbs at higher flow rates.
Consistent pressure results in smoother running, better performance, easier
tuning and reduction in fire hazard due to overflowing float bowls.
Anyone want to try a test of the max and min psi under enthusiastic driving?
Say an MGB accelerating uphill vs braking on a steep downhill.
Don
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