Suck, Squeeze, Bang, Blow...

Physics

"Aviation is proof that given, the will, we have the capacity to achieve the impossible." --Eddie Rickenbacker: My brother—a performance engineer in the aerospace sector—once gleefully asked me if I knew how a jet engine worked. I—a history teacher who studied religion and anthropology in college—admitted I did not. He said with a naughty chuckle, "suck, squeeze, bang, blow!" I blinked at him with no emotion on my face. He repeated himself, "You get it? Suck, Squeeze, bang, blow!" ... ... ... I didn't get it. I mean, of course I understood that one brother saying this to another brother was inappropriately funny, but I had no inkling how it actually described what a jet engine was doing. He said something like: "The air get's sucked in, gets compressed with fuel, is lit on fire, and the resulting expanding air blows out the back of the jet... Thrust!"

“I love old things. Modern things are so cold. I need things that have lived.” -- Barbara Hulanicki: I have delighted in telling my mechanically minded friends over the years what I had learned about jet engines. It never surprises them. They all knew what I had not known for so long; it turns out the saying my brother taught me is true for non-jet engines as well. I "got it" intellectually of course once it was brought to my attention, but I did't fully understand until I studied and rebuilt my first carburetor for my '74 Honda CB360.

Internal Combustion: There is is big, heavy, metal, "thing" at the core of my motorcycle called an engine. I know there are gears and oil and moving parts. There are valves and seals and heavy bolts. There are also pistons in there that rise and fall in little cylindrical rooms that are  repeatedly filled with gaseous fuel and lit off with a spark that makes an explosion which, in turn, moves the piston (expanding the "room", the force of which is redirected and harnessed as "drive." What an interesting development of the engine from steam; no more heated and expanding water vapor, but mini explosions of gaseous fire!

40+ year-old gunked and dirty dual-carbs

It's the little things: The engine is fantastic in all it's complexity, but that is not surprising given it's central location, weight and size. It's the small parts the are between the fuel line and the engine that were more of an enigma to me; the carburetors. Carburetors are like like little mysterious magic boxes.

How Things Work: Here's how carburetors work in the most simple, religion-major-who-knows-nothing-about-engines way of explaining things: When the starter (electrical) or crank (manual) turns something mysterious in the engine that moves the pistons, they (the pistons) create a vacuum in the engine which pulls air in from the outside world, through the air filters, and then through the carburetors (in parallel as is in the case of my Honda). The flowing air is the key "worker" in this magical process; the pathway it takes through the carburetors is almost hourglass shaped. There is a seemingly mystical and esoteric area of study that explains a set of wizardly phenomena called physics. One concept in this field is called Bernoulli’s principle: air passing through the hourglass shape needs to speed up to "get through the constricted path," which in turn causes a new mini-vacuum, which in turn pulls fuel through a series of appropriately "dialed-in" holes ("jets") from a simple reservoir. The more "open" the the throttle is, the more air passes through the system, therefore the greater the vacuum, and subsequently the greater the amount of fuel that is being mixed with the greater amount of air to make more frequent explosions in the engine to make the bike go faster. This proper air-fuel mixture "thing" that the carburetors does is purely mechanical. There is no electricity in this part of the system; there is no computer chip controlling it; there is no "brain" so to speak of. It is a series of reservoirs, chambers, canals, and gates that is all controlled essentially by tuning the system, and then just opening and closing the air intake by rolling on or off the throttle. Amazing!

Clean

"Design is a funny word. Some people think design means how it looks. But of course, if you dig deeper, it's really how it works." --Steve Jobs: The love that my 1974 dual carbs received included a long sit all all metal parts in a chew-dip bath, new gaskets, jets, and floats. All in all pretty simple once I moved past the mystique of all the little pieces. Several jets allow different amounts of vacuum to draw ever more amounts of fuel into the system. Simple flaps choke the air or let it flow. Rubber gaskets and seals keep the right parts sealed up. And the clean metal means there is no "gunk" inhibiting the flow of fuel through the small canals and jet holes. I took detailed photos of all the parts as they came off to help take the guesswork out of putting them back in the proper order. What started as the most enigmatic piece of my bike, turned out to be fantastically simple and beautiful.

And we were ready to go!: The carbs were placed back on the engine, ready to deliver their fuel/air mixture magic, and Joe ran...

For seven seconds...