I picked up a 1980 mini 1000 a month ago and I've been doing some general maintenance stuff. While changing the air filter, I began pondering the warm air intake system... is this necessary? I grew up with fuel injection, so all this carburetor stuff is new to me. My FI knowledge says rip that crap out and get some cool air into the filter box, but I don't want to act without seeking input first. I didn't have a lot of luck googling it, but that could be because I'm not using the correct technical terms... What do you think?
Stock air intake system
The top of the metal oval is spring loaded, I assume it opens up under load to allow fresher air from the engine bay to come in (instead of up from the manifold area). The duct extends down to the exhaust manifold.
It pushes in pretty easily
The "warm air duct" as it is attached to the exhaust manifold. Also note the spring portion of the flapper valve sticking out of the right side of the metal oval, definitely not good for air flow!
Probably not relevant, but the SU carbs on my minis had heater bands around the pots. Canadian cars,so it may have been to prevent the carbs from freezing. I suspect the hot air duct might be there for the same reason.
I believe that is a bimetal spring, and as it warms up, it will open the flapper valve.
Keeping the manifold warm on carbureted engines helps maintain the proper atomization of the fuel. As the air passes through the carburetor and has fuel added to it, the air cools significantly, up to 100* F in some cases. If you have a cold manifold as well, the fuel will condense and stick to the manifold walls, resulting in garbage idle and cold weather running. On older Chevy I-6 engines, this is why the exhaust manifold and intake manifold are intertwined...
Yeah, that should be a bimetal spring for exactly the reasons you mention.
A lot of the old carb cars had similar setups. I never had issues after removing them, but I live in Georgia.
If you're in cool, humid country without the warm airt intake, you can get carb icing - ice literally forms on the carb and manifold and the engine will die. Happened to me once in northern New Mexico in 45 degree weather in the rain with a '75 Toyota pickup - had to let the ice melt before continuing. If you live in Phoenix, probably doesn't matter.
More importantly, it's not doing any harm and your EFI knowledge is exactly backwards here because of the cooling effect of the atomizing fuel 
I'd leave it.
Thanks for the information! For the record, I'm in the Blacksburg, VA area (southwest VA). I would think the intake manifold being above the exhaust manifold would aid in heating, but I will leave it as is.
Time to start reading more about carbs!
Carbs are weird. The best thing about them is that hitting them with a hammer is a legitimate repair technique.
just as a reference point, the engine you have is a BMC A series, which is the same as my bugeye sprite (engine from a 73 spridget).
There is no concession for warm air on the spridget. (stock phot from internet, not my car, but those are factory air cleaners). You could probably pull it off and pop some K&N's on it if you dont drive it in winter. Keep in mind that the exhaust is on the same side of the head on these engines with a thin metal heat shield, so Icing wouldnt be too common..
Keith Tanner said:
Carbs are weird. The best thing about them is that hitting them with a hammer is a legitimate repair technique.
My dad watched me whack a Holly carb with the handle of a Snap-On ratchet to fix a stuck needle and said "Wow, Snap-On makes a tool for everything!"
My first carburetted car was my 1967 Land Rover. I literally dragged it out of a barn and got it back on the road. I took it to the Ottawa Valley Land Rover club "birthday party" meet which was the first time it left town. That night in the campground, it developed a running problem. I was under the hood, cluelessly prodding at things when one of the club gurus came wandering out of the dark. I voiced my complaint. He reached out and tapped the side of the carb with his Maglite, then disappeared into the night leaving behind a happily chugging Land Rover.
I was awestruck.
I had a car that had manifold heat but when really cold the carb would ice up.
I devised a method to put some heat to the air cleaner.
Kind of off topic, but I had a CFI 3.8 liter '84 T-bird once that would like to stick the throttle when it got below -10°F out. I discovered this while trying to drive it. The throttle seemed a little sticky pulling out of the driveway, so I did what I was taught, which was give the pedal a good whack. Of course, now, the throttle was stuck to the floor, which was cool, because there was about 8" of drift snow across the road. I let it be insane until I got it through the drift, then turned off the key and popped it into neutral. As I pulled off into a small parking lot, I heard the pedal pop up. Everything was fine. I started it up, and went on my way. From then on, whenever it was real cold, I would start the car, and see if the pedal was hard to push at all. If it was, I would wait a minute, and then shut it off, then lay my foot on the pedal. After about 20-30 seconds or so of the heat from the engine going up to the throttle shaft, it would free up, and it would be fine from then on.
[/hijack]
Keith Tanner said:
He reached out and tapped the side of the carb with his Maglite, then disappeared into the night
Great story. I just put two old school D-cell Maglites into our "yardsale" box last weekend... perhaps I need to retrieve one for future carb repairs...
We need a proper write up on this mini in the build section
That car is so nice Please don't mod it. But the reason for Carb Heat Is well Explained here. In N.Va. I would leave it on and also warm the engine some before driving it, Year round. this issue of warming an engine has been discussed recently, I myself am for it.
