What is this part?

[drddan]

Pulling off the Festiva carb to put on a Weber, this was between the carb and the intake. Anybody know what the heck it is? I'll using it to make an adaptor for the Weber.




What is that hex thing and what does it do?

[htchbck]

Not an expert on carbs, but I bet its got something to do w/emissions control. Somehthing to do with the EGR maybe?...

[m715]

It is a preheater which is energized for a short time at startup to help in cold weather atomization of the fuel, reducing emissions.

Michael

[htchbck]

Well, the first half of my guess was right at least lol its for emissions.

[drddan]

Thanks! Yeah, it usually has to be emissions related. What I figured too.
A preheater, huh. Looks like that would be it. Its not going back on , just a template for the adaptor I have to make. Cant get one anywhere. FMS dont make anymore, no one on here seems to have one. (at least no ones answered my WTB post)
Picked up 2 pcs of 3/8 thick aluminum plates today. Got the gasket from the Weber and also the Festy plate in above pics, so its time to start making the adaptor now. I may post up a blueprint/sketch of it when i'm done.
The hole patterns between the Weber and Festy interfere which dictates a 2 pc adaptor.

[drddan]

I cant believe the number of vacuum hoses and wires that are on this Festy!
Be nice when its done, most of them will be gone!

[m715]

I bought the last one Roger had a few years back, and have it around here somewhere..... IIRC, it is out of a machined block of aluminum about 4" thick.

Michael

[jmye1524]

The hole patterns between the Weber and Festy interfere which dictates a 2 pc adaptor.

Keep us posted... this is what I came up with for my Holley







.

[drddan]

IIRC, it is out of a machined block of aluminum about 4" thick.

Michael

4" thick! Holy crap! That IS thick! 'Mine is half done. The part for the festy intake is done. It will bolt to festy intake with flat head screws in place of the studs now there. The Weber adaptor will bolt to the Festy adaptor, which will be drilled/tapped for studs with the Weber hole pattern. Total 3/4" thickness.

[drddan]

Whoa! Apparently a little height is a good thing. The 3/4" adaptor is a little lower than I would like. The choke is almost sittin' on the valve cover.
Didnt dawn on me until I was was makin the adaptor, and set the carb in there. Noticed it was setting way to low.
Can still use the Festiva pattern piece I just made, but on the Weber part of it, I am gonna use 1" thick. Might even start new with 2 pc of 1" for a 2" thick adaptor.

[AlaskaFestivaGuy]

That part (about which this thread started) may be for more than emission control. It heats the air going into the carb, which reduces the tendency for ice to form in the carb throat as the air expands (and hence cools below the freezing point).

Carb'd airplane engines all have a provision to heat incoming air during low power settings (e.g. descents) by directing incoming air through a shroud over the exhast pipe before it hits the carb. It's a PREVENTATIVE system -- the pilot pulls a knob to redirect the incoming air anytime he drops below a particular power setting, or if he feels any roughness in the engine. It generally will not melt significant ice that has already formed in the carb. Since warm air is less dense than cold air, it robs the engine of a bit of power, so is only used in the above circumstances, or sometimes when flying through rain. When the air is redirected in this way, it also bypasses the air filter (in case the filter has iced over and is restricting air flow). For that reason (unfiltered air), it is never used on the ground.

Carb icing can happen with outside temps as high as 68-70F!

It would be interesting to trace the wiring and see if the heater is turned on only under certain conditions (low temp, low power setting, etc.)

[drddan]

Interesting..... food for thought. If I need it, it is still in good condition and can still be used. It made a very good template for fabrication of the adaptor.

[bravekozak]

icing

My first experience with icing on the butterflies was when I blocked the heat crossover under a Holley double pumper. It's usually when the air has a lot of humidity and it's just above freezing. I would have to run the engine for about four minutes before setting out, or risk stalling.

[AlaskaFestivaGuy]

Yes, high humidity triggers carb icing. When the air cools (due to expansion as it's drawn into the low-pressure air inside the carb throat), it cools. If it cools down to below freezing, and that point is below the dew point, you're ripe for icing. Dew point is the temp to which the air must be cooled to be "saturated" -- 100% humidity. That's why pilots check the "temp/dew point spread" -- it it's only a few degrees, any cooling of the atmosphere (say, as night approaches) will lead to fog, even if that's well above freezing.

I'd leave the part in the car. It was put there for good reason.

[drddan]

Well. I'm gonna think about that. Anybody else encounter the icing problem?
There are a few peeps on here that have Weber carb's. Did any of you re-use the heater plate on your Weber. If not, were there any problems without it. One issue I foresee with using the heater plate is that it is the Festiva hole pattern. On the adaptor i'm making, the heater plate will have to go under the adaptor plate for the Weber. This will locate it 1" below the Weber as the Weber side of the adaptor will be 1" thick. It would be sandwiched between the 2 plates making up the adaptor. Gas will also be going through that hex shaped aluminum piece you can see in the photo. Seems to be a restriction to gas/air flow to me. I would prefer NOT to use the heater plate.
Some good sounding advice, though, and i'm taking it into consideration.
Thanks.