Quiz time again. I have two problems with my son's street Spitfire, 72
MKIV. The first problem, really more of a validation I hope is related to
the carbs. I removed the stock single Stromberg and replaced it with a pair
of HS2 SUs.I was tweaking and balancing them, they were running rich. When
I rev'd the motor up, I noticed a squirt of gas from a small hole, on the
firewall side carb, just under the fuel inlet. I pulled the float and
checked it's function, when the float was almost level, the valve would
close and keep me from blowing through it. The front carb worked in a
similar fashion. I never noticed the hole before, looks like it meant to be
there, but is it , as I suspect, a vent hole for the fuel bowl, and not an
over pressure relief port? I'm guessing that I just need new needle valves
and/ or a float and I should be good to go. But before I order the parts
and waste a week, is the stock fuel pump, designed for the Stromberg, too
powerful for the SU floats? Should I be changing the stock pump for one
from a duel carb model too?
Question number two. The ballast resistor broke, don't know how but we had
a problem starting and I found the ceramic rod and wire broken. I picked up
a generic one at the local parts chain but I still have the problem, the
car will only run on the start up circuit. As soon as I stop turning the
starter over, the ignition dies (verified by timing light). I put a meter
on the input to the resistor and with the key on, I have ~ 12.8V and 12.5V
on the coil side. The resistor measures ~ 200 ohms. All the wires back to
the ignition switch look good and ohm out clean, but the car won't run.
Do I have a problem with the replacement resistor? I've used this type
before on the race spit motor but I didn't want to start swapping parts
from that, I have a dbl race next weekend. Could I have a bad connection
somewhere, only good enough to show 12V potential but not pass enough
current to fire the coil?
Related to the debug of this problem, I changed points, set the gap and
timed the motor. I also swapped coils with a spare. If I hot wire the
starter circuit, jumper wire from the battery to the coil, the car will run
forever. (this just got me thinking, I'll hot wire the feed into the
resistor tomorrow and see what happens)
I can't find a value for the ballast resistor, does anyone know what
values (Ohms and voltage drop) I should be seeing?
thanks in advance
mike h.
G. Michael Harmuth
Software Engineer
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