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At the Rotorfest, I showed some data concerning fuel pressure
instability with my Mallory adjustable regulator and the improvement as
a result of installing the non-adjustable OEM Mazda regulator.
Recently, I noticed that Mallory came out with a rebuild kit (part#
3178) for the 4305M/4307M regulator which appeared to be a different
design rather than simply replacement parts.
Out of curiosity, I ordered the kit to see if the regulator would
actually regulate with the new parts. The picture labeled "new parts
bad seat" shows what I received. The teflon seat looked like it had
been hacked out with a dull serrated knife. I coated the ball with a
magic marker and placed it on the seat so the points of contact would
show up black in the picture. There was no way that the parts would
work as received.
It was simple enough to repair the seat in the lathe and the results are
shown in the picture labeled "new parts repaired seat".
The picture labeled "old and new parts" show the old parts in the lower
left and the new parts in the lower right. The old parts had already
been altered from using a rubber X-ring seal to using a teflon seal with
much less friction in the bore of the cylinder attached to the
diaphragm. This had resulted in a decrease in hysteresis from over 15 psi to about 5 psi. When installed on my fuel injector test bench, the old parts as shown
would exhibit the hysteresis and sometimes the fuel pressure would
oscillate turning the pressure gauge needle to a blur going from about
15 to 60 psi and back very rapidly.
With the repaired new parts installed and using only the large outer
spring, the fuel pressure was absolutely stable at any pressure I set it
to. When set at 40 psi, the fuel pressure followed manifold pressure
changes applied to the sensing port smoothly with no hysteresis. This
is the result of only a few minutes running on the test bench, but the
improvement in fuel pressure regulation is very marked. If you have the
old style parts in a Mallory regulator and the fuel pressure isn't as
stable as you expect it to be (Bobby?), the repair kit may be something
to consider (assuming they send you usable parts). The last picture labeled "assembled regulator" shows the jam nut with a
gasket between it and another nut with a cap welded on it which
eliminated the air leak through the threads of the adjustment rod.
For what it is worth...
Steve Boese
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