Hello all,
Been trying to earn 2 paychecks and finish the plane so slow to respond on the
net.
First: carb icing typically does not occur above 70 degree F temps, and
high humidity days. If you have carb icing look at both the humidity for the
day AND the temp at altitude. Someone already explained it technically, but in
simple terms the gas introduced into the carb venturi, coupled with the temp
drop associated with the velocity increase in the venturi together produce the
ice which builds up and stops flow of fuel. The engine heat is not enough to
melt this ice, which is the reason that exhaust mounted "cups" are used to
apply heat to the carb venturi when icing is experienced. The early V8 engines
did NOT use heat riser tubes off the exhaust to prevent carb icing, but rather
had them for assisting the engine in warming up, by causing the incoming air to
the carb to be drawn off of the rapidly warming exhaust to warm the air/fuel
mixture to prevent separation when the mix struck the cold intake manifold.
Gradually the engine heat, through water cross over in the intake manifold
ends, and exhaust heat cross over under the carb would provide sufficient
heating to prevent separation, and the heat riser from the exhaust would be
shutoff through the use of a heat controlled vacuum valve. The problem was
that early engines were not very good at keeping themselves cool, so thermostat
temps were kept low, which allowed for icing, even though the engine was "hot".
This inability to properly cool also lead to percolation of the fuel still in
the line or vapor locking as we all know it. This happens in almost every
certified fuel injection engine, due to hot soak. An easy way to eliminate this
is to use an auxiliary fuel pump to insure that liquid fuel fills the line not
gas, by running this pump for approximately 10-15 seconds before attempting
startup. Then you know that enough fuel mist is being applied, instead of the
excessively lean amount during vapor lock. All carb engines should have a
certain amount of engine heat applied to the carb for proper atomization of the
fuel mixture, or commonly, fuel mixing. So yes Serge apply heat.
Colin & Bev Rainey
KR2(td) N96TA
Sanford, FL
[email protected]
or [email protected]
http://kr-builder.org/Colin/index.html
