alternate carb heat

Steelgtr62 wrote:

Some British engines used an oil passage through the carb venturi, a far more
elegant solution. However using fuel injection or mounting the carburetor on
top of the engine instead of underneath would largely obviate the problem.

Fuel injection will help a lot, but mounting the carb on top makes
almost no difference.


Matt

Matt Whiting wrote...

...but he may be referring to turning on the carb heat
after he's already accumulated enough carb ice to noticeably
decrease his RPM.

Yeah, that's it. g No, I'm afraid UltraJohn was right.
I haven't seen anything remotely resembling carb ice,
and from what I've heard it's not very common in RVs.
I get a very slight RPM *drop* with carb heat, presumably
to a slight temperature *rise* from switching to undercowl
air.

Dave 'cold throat' Hyde

"My wallet's fat and so is my head" - Greenday, 'Walking Contradiction

Matt Whiting wrote in message ...
Steelgtr62 wrote:

Some British engines used an oil passage through the carb venturi, a far more
elegant solution. However using fuel injection or mounting the carburetor on
top of the engine instead of underneath would largely obviate the problem.

Fuel injection will help a lot, but mounting the carb on top makes
almost no difference.


Matt

The Gipsy Major took its carb heat from up next to the
crankcase. As with using undercowl air, the time between startup and
useable heated air is too long and carb ice can form while warming up.
We see carb ice shortly after startup rather regularly here, and
we live in fairly dry country. Need to pull carb heat soon after
startup some mornings. It's a good thing the exhaust piping heats up
quickly.

Dan

Thanks for the insightful help, I planned to install some sensors to
check the rise. I think I will glue one rite to the outside of the
carb at the intake for as realistic a measurment as possible.
I use those little automotive outside air temp sensors I buy from
Canadian Tire, I noticed Wally wallmart has them as well but the ones
I bought from wally were celsius only, irritating but not
unsurmountable. They have about six feet of wire and a sticky back
wich seems to hold well.
God bless all the little borocrats who consented to give us the
homebuilt movement.

ray

On 19 Oct 2004 16:55:42 -0700, (Dan
Thomas) wrote:

Matt Whiting wrote in message ...
Steelgtr62 wrote:

Some British engines used an oil passage through the carb venturi, a far more
elegant solution. However using fuel injection or mounting the carburetor on
top of the engine instead of underneath would largely obviate the problem.

Fuel injection will help a lot, but mounting the carb on top makes
almost no difference.


Matt

The Gipsy Major took its carb heat from up next to the
crankcase. As with using undercowl air, the time between startup and
useable heated air is too long and carb ice can form while warming up.
We see carb ice shortly after startup rather regularly here, and
we live in fairly dry country. Need to pull carb heat soon after
startup some mornings. It's a good thing the exhaust piping heats up
quickly.

Dan

Ray Toews wrote in message ...
Thanks for the insightful help, I planned to install some sensors to
check the rise. I think I will glue one rite to the outside of the
carb at the intake for as realistic a measurment as possible.
I use those little automotive outside air temp sensors I buy from
Canadian Tire,

-------------------------------------------------------------------

Dear Ray (and the Group),

Take your outside air temp sensor and hit it with a hammer. Okay,
okay... squeeze it with a pair of pliers. IF (Big IF) IF... you're
lucky, inside you will find a thermistor about the size of a grain of
sand; the the tiny bit of **** that seems to be welded to the wires.

To measure temperature at the carb, drill a hole in it large enough to
accept the thermistor. (#80 works for the little thermistors.) SOP
is one hole just above the throttle plate (if you have a throttle
plate). (If you want to measure inlet air, put a thermistor on the
carb-side of your carb heat box.) Now put a piece of tape over the
hole on the INSIDE of the carb and go find yourself some metal-filled
epoxy. The Good Stuff comes from Kodak, contains silver and transfers
heat with virtually no loss at all. Mix up a dot of it, dip the
thermistor into the epoxy and plug it into the hole. Now let it cure.
(Don't forget to remove the tape.)

You may install a suitable connector, if you wish. Should I mention
that it's a good idea to only drill where the carb is solid metal?
(Nah!)

A carburetor makes a nice refrigerator. Outside air temp has
surprisingly little to do with it. The pressure drop across the
venturi (traditional carb assumed) and gasoline's endothermic
change-of-state is enough to put frost on a can of beer quick like a
bunny. With a suitable temperature probe in place you can sit there
warm & cozy in the cockpit and see it all happen long before the
engine starts running ruff and the Bad Silence ensues. (You may want
to pull out that red knob over there...)

-R.S.Hoover

May want to test the thermistor after you free it from the evil probe and before you capture it in the refrigerator....


"Bob Hoover" wrote in message ...
Ray Toews wrote in message ...
Thanks for the insightful help, I planned to install some sensors to
check the rise. I think I will glue one rite to the outside of the
carb at the intake for as realistic a measurment as possible.
I use those little automotive outside air temp sensors I buy from
Canadian Tire,

-------------------------------------------------------------------

Dear Ray (and the Group),

Take your outside air temp sensor and hit it with a hammer. Okay,
okay... squeeze it with a pair of pliers. IF (Big IF) IF... you're
lucky, inside you will find a thermistor about the size of a grain of
sand; the the tiny bit of **** that seems to be welded to the wires.

To measure temperature at the carb, drill a hole in it large enough to
accept the thermistor. (#80 works for the little thermistors.) SOP
is one hole just above the throttle plate (if you have a throttle
plate). (If you want to measure inlet air, put a thermistor on the
carb-side of your carb heat box.) Now put a piece of tape over the
hole on the INSIDE of the carb and go find yourself some metal-filled
epoxy. The Good Stuff comes from Kodak, contains silver and transfers
heat with virtually no loss at all. Mix up a dot of it, dip the
thermistor into the epoxy and plug it into the hole. Now let it cure.
(Don't forget to remove the tape.)

You may install a suitable connector, if you wish. Should I mention
that it's a good idea to only drill where the carb is solid metal?
(Nah!)

A carburetor makes a nice refrigerator. Outside air temp has
surprisingly little to do with it. The pressure drop across the
venturi (traditional carb assumed) and gasoline's endothermic
change-of-state is enough to put frost on a can of beer quick like a
bunny. With a suitable temperature probe in place you can sit there
warm & cozy in the cockpit and see it all happen long before the
engine starts running ruff and the Bad Silence ensues. (You may want
to pull out that red knob over there...)

-R.S.Hoover

Just use a standard K or J type welded junction type thermocouple (i.e. two
wires welded together in a small bead). I would be cautious of any other
type of sensor ... they may have too much mass and will introduce lag or
damping into the readings because of the time required to heat the mass of
the sensor housing.

Also don't bond the thermocouple to the carby housing. You want to measure
the air temperature, not the temperature of the metal inlet flange to the
carby.

Just stick the thermocouple wire into the inlet area - depending on the
engine you can loosen a cable clamp in the alternative air system and just
slide it in and retighten the clamp. I would slide in approx 1" of
thermocouple wire so that the thermocouple is somewhere near the middle of
the inlet hose.



Ray Toews wrote in message ...
Thanks for the insightful help, I planned to install some sensors to
check the rise. I think I will glue one rite to the outside of the
carb at the intake for as realistic a measurment as possible.
I use those little automotive outside air temp sensors I buy from
Canadian Tire, I noticed Wally wallmart has them as well but the ones
I bought from wally were celsius only, irritating but not
unsurmountable. They have about six feet of wire and a sticky back
wich seems to hold well.
God bless all the little borocrats who consented to give us the
homebuilt movement.

ray

On 19 Oct 2004 16:55:42 -0700, (Dan
Thomas) wrote:

Matt Whiting wrote in message
...
Steelgtr62 wrote:

Some British engines used an oil passage through the carb venturi, a
far more
elegant solution. However using fuel injection or mounting the
carburetor on
top of the engine instead of underneath would largely obviate the
problem.

Fuel injection will help a lot, but mounting the carb on top makes
almost no difference.


Matt

The Gipsy Major took its carb heat from up next to the
crankcase. As with using undercowl air, the time between startup and
useable heated air is too long and carb ice can form while warming up.
We see carb ice shortly after startup rather regularly here, and
we live in fairly dry country. Need to pull carb heat soon after
startup some mornings. It's a good thing the exhaust piping heats up
quickly.

Dan