If the diaphragm were to stiffen with age, that could result in higher
pump pressures. Never seen that actually happen, but theoretically it's
possible.
Howsomeever, as I recall you initially started with the ZS. That
carburetor does not seem as sensitive to over pressure as the SU's are.
Not that the ZS is immune, it's just not as apparent a problem.
Personally, I suspect a whole lot of ZS problems come from excessive
fuel delivery pressure.
The Paul Harvey "rest of the story" is that many of the replacement
mechanical fuel pumps produce too much fuel pressure for these
carburetors. They produces pressures of 4-7 psi, which is fine for a
Japanese or American carburetor, but way too much for an LBC. Using an
inline pressure regulator has solved the running problems of many an
LBC, including my own.
>>> "Ken" <sdspitfire@sbcglobal.net> 10/07/03 07:09PM >>>
Anyone ever had a mechanical fuel pump suddenly develop higher than
normal
pressure ? I can understand the diaphragm rupturing and the pressure
dropping to zero, but is there a failure mode causing higher pressure
?
The reason for the question, I'm having difficulty getting the new
engine to
idle properly. Went ahead and pulled the dual HS4's and replaced them
with
dual HS2's and the problem remains. Both carburetor sets worked
perfectly on
the old engine. Been through all the normal troubleshooting procedures
to no
avail. The problem could be fuel getting past the needle and high fuel
pump
pressure could be the cause.
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