On 26 Mar 97 12:50:15 PST KILE_PAUL@aphub.aerojetpd.com (Paul D Kile)
writes:
>Induction heaters ..... heat the induction charge of fuel and air, just
inboard of the throttle plate. These were used to prevent carburetter
icing at low temperatures.
>
> ..... phenolic insulator spacer between the carb and the manifold. If
the spacer has a little thimble shaped housing with a wire attached, you
have an induction heater. ..... the thimble houses a thermostat that
energises the heater below about 36 degrees F. ..... The SU
installations also had heating bands around the carburetter piston domes
.....
My '69 Austin America (long gone) 1275 with single SU had an induction
heater. I think the band heater on top was an after thought when the
throat heater didn't quite cut it in really cold weather. Mechanics at
the MG dealer figured the band heater was a lot more effective, given a
minute to warm up the carb before starting. Cold start procedure was to
switch on the ignition, take a minute to clean ice off the windscreen,
then start it right up.
I don't think it was an icing problem so much as lack of vaporization of
the fuel. On cold start the fuel from the mixing jet would just trickle
down the bottom of the throat, run through the intake manifold and puddle
on top of the pistons. No vapor, no fire. Without the carb heater that
car would never start after a night outdoors with the temperature below
0dF. At 1dF it would start, at -1dF, no way.
As I recall, the thermostat was set to actuate at 20dF or colder, and
should shut off when the carb warmed up to that temperature. When the
air temperature was about -10dF it took a long time for the carb to warm
up to 20dF. Power for the band heater was tapped off the same bi-metal
thermostat that powered the throat heater. I reckon the added load of
the band heater was too much for the contacts in the thermostat. It was
good for just one start at -10dF, after which the thermostat failed so it
wouldn't start the next time. After replacing the thermostat about three
times it was common to wire in a toggle switch.
Barney Gaylord
1958 MGA -- twin SUs without heaters and starts at -10dF
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