Charlie R wrote:
< Didja know that many electronic fuel injection systems have a "cold
start valve" on them? I's the same thing, y'see. When I was a software
analyst, the elegant solution was usually the simplest one.>
Charlie,
The starting carb is similar to the modern cold start valve. However, I
believe that the computer varies the cold start valve open time based on
engine parameter just like any other injector. While you can set the HD
starting carb for a base leakage rate but there is no other adjustment. In
fact, since it operates off manifold vacuum it is actually bass-ackwards
and feeds more fuel under high vacuum conditions. From what I understand,
many old Jag owners add a manual switch to the solenoid to prevent flooding
on "semi-cold" startups and during extended cold idle.
On a similar note, the SU may have another unintended cold air enrichment
device. When cold the dashpot damper oil is thicker and provided more
enrichment on acceleration. A person could spend a lifetime finding the
perfect multiweight oil to tune this "feature."
Which brings us back to reality. Modern cars get away with varying
everything because computers are fast, car companies can afford dyno time,
and feedback devices (exhaust oxygen, knock, ?) are available. For us poor
schleps trying to keep a 40 year old car on the road, simplicity is a good
thing. Like any motorhead engineer, While writing these posts I started
working out how I could add a bimetallic spring to the HD6's and get fuel
delivery that varies with the three major factors. However, I could spend
a lifetime varying everything to get it all to work and, lacking a more
accurate feedback method than reading plugs and the seat of my pants, the
odds that the result would run better than what I have are slim to none. I
figure that, on the list of things that need to be done, this ranks right
down their with braiding my ear hair for formal occasions.
Regards,
Bill Eastman
61 MGA who suffers enough already from my loving "adjustments"
58 Jaguar XK150 parts filling all available space.
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