D-F
Dammits = Those devices on the back of your pins that you will almost always drop. Can be used synonymously with Jesus-clips
Detonation = See Pre-Ignition
Drag Bars: Low, flat, straight handlebars
Drag Pipes = These were short exhaust pipes that ran low along the frame.
Duals = 2 separate Exhaust pipes, i.e. one each for front & rear cylinder.

Ear's = Air boxes (i.e.: on a Kawasaki VN750 or VN1500A or any Virago)
Engine = Mill,
Engine Guard = Crash Bar
Exhaust System = Pipes

FAR = Factory Authorized Repair
Fat = Too Rich Fuel Mixture
Fiddly-bits = Those chrome do-dads all over saddle bags and seats.
Fishtails or Fishtail Muffler = The exhaust tip or the end of a muffler looks like a Fishtail from the side and usually straight pipe's with Fishtail tips had a narrow exit for the exhaust where no night stick could fit to check for baffles in the exhaust pipe. - Tom Roop
Flower Pot = A cheap helmet non snell-approved head protection device.
Flycatcher = Kuryakyn Hypercharger
French = An old custom car and bike term that refers to mounting a device, a light, usually, deeply recessed into the bodywork, "frenched-in," and peeking out from within a sort of tunnel, completely recessed below the surface of the surrounding bodywork, presenting only a sudden, clean circle through smooth the surface from which the light appears
Frisco'ed/Frisco style = Style when a gas tank is mounted right along the top of the backbone.
Frisco Pegs = railroad spike highway pegs
FUBAR = which is a very old slang acronym meaning "F**ked Up Beyond All Repair." Pertaining to the sad, inoperable and unfixable state of someone's bike or engine or whatever.
Fuel Management System = Carburetor

G-I
GearHead = Any TRUE mechanic, not just the weekenders
Giblets = Chrome Accessories
Giggle Gas = Nitrous oxide

HairDryer = Turbocharger
Harley Wrench = Hammer
Helmet = Skid Lid, Brain Bucket
HippoHands = Naugahyde w/ fleece innerthat went over handlebars so you didn't have to wear gloves (eg. Craig Vetter)
Hogwagen= A custom-built trike in which a Harley-Davidson front end and frame is grafted to a Volkswagen drivetrain (subframe, engine and transaxle).
Hosed = Worn or broken beyond repair
Indie Shop = Independent, not franchised

J-L
Jesus Clip = A small clip that you WILL drop, followed by "Oh Jesus", 'cause you know you will never find it.
Jiffy = Side Stand
Jugs = Cylinders

Kinnipullin Pin = clevis pin
Knucklebuster = open end wrench

M-R
Marquis deSaddle = A highly uncomfortable motorcycle seat
MANF = "Multi Adjustable Nut F**ker", aka adjustable spanner! (UK)
Mechanic = Wrench,
Megaphone = Goes onto the end of the exhaust to help tune it
NEW Mexican socket set = crescent wrench
Mill = Engine

New Skin = New paint job

Oil Pressure Warning Light = Too Late Light
Oil Bag = Oil tank
One-Off = one-of-a-kind fabricated part
OPG = Oil Pump Drive Gear (used normally to refer to the infamous plastic oil gears in Kawasaki Vulcans)

Pads = Tires
Passenger Backrest = Sissy Bar,
Passenger Pad = Pillion Pad
Pee-Pad = "The little pad put on the rear fender behind the solo seat to accommodate (but not for long) a passenger. Got the name because chicks will eventually pee on it if they ride (bounce would be a better term) on the fender of a hard tail for any extended period of time."
Period Custom = A term heard in antique motorcycle circles, referring to bikes which are not "restored" to factory specifications, but built today with modifications original owners of the bikes might have made, like adding Flanders risers or bars, "bobbing" rear fenders by removing the hinged tailpieces or removing the front fenders and front brakes entirely, or hopping up the performance with reground stock cams or other early-style engine modifications.
Pipes = Exhaust System
Plugs = Spark Plugs
Ports = intake & exhaust valve openings
Pot = Carburetor
Pre-Ignition = Pre-ignition is when the intake charge is ignited too early. The combustion pressure exerts large forces on the upward traveling piston and can destroy the engine. On the other hand, detonation can occur at any point during the combustion process. It is basically a violent and uncontrolled explosion in the combustion chamber. Although folks commonly refer to combustion as an "explosion" it is actually more appropriately termed a "controlled burn". Explosions in the combustion chamber are undesirable, and the violent release of energy can also destroy an engine. Pre-ignition can sometimes lead to detonation because the premature burn is simultaneously compressed. Pre-ignition and detonation are both bad news.
-----Detonation is usually caused by a *lean* A/F mix. (vacuum leaks) or improper jetting. Also by low octane fuel, over-advanced timing, lugging of engine, and of course excessive carbon in the combustion chamber. A rich mixture can lead to detonation due to excessive carbon build-up in the combustion chamber decreasing its volume and raising the compression excessively.
Puffer = Supercharger
Pull = Ability to accelerate
Pussy Bar = Sissy Bar (passenger backrest)

Raised Tranny = Harley bikers would use a spacer to raise the transmission on their bikes so when riding in dirt and mud to try to keep the primary cover away from anything that might knock into it.
Rolling Basket = Basket case bike, fairly intact but does not run, needs work
Rolling Chassis = Incomplete project, has everything but mill & tranny
Roun To-It = "instrument used to delay a job e.i. one of these days i'll get around to it. ha ha"
Rocker-Clutch or Rocker Clutch Pedal = This term was used to describe the foot clutch pedal's that rocked back and forth on a central pivot point hence the term Rocker-Clutch) and the rider would step on the front toe section to disengage the clutch and the rear section with the heal of your boot to engage the clutch.
Rocker Clutch and Harley/Indian differences- During the heyday of the Indian vs Harley-Davidson wars, in the 20s,30s and 40s, the two largest American motorcycle manufacturers seemed to strive to do anything possible to make their products opposite in operation from each other. I.e.: Harleys' throttles were on the right handlebar (the normal place), but Indians' throttles were on the left; Harleys were shifted by the left hand, Indians by the right hand, and Harley clutches engaged toe down, and disengaged by stomping the heel down. Indians were just the opposite: toe down to disengage, heel down to go. A few very experienced riders who set their minds to learning how could jump off one and onto the other make bike and ride away without killing themselves, but it took a great deal of self-training and practice. And concentration. The police departments, and the U.S. military, tended to prefer Indians, if only because a right-handed rider could draw and fire a sidearm, or salute an officer, with his right hand on an Indian, while keeping his left hand on the throttle and guide the bike. This fact was appreciated by the leadership at Harley-Davidson, who offered a kit of alternate parts in the 1930s (when times got tough during the Great Depression, and increasing police fleet sales became important to keeping the company solvent), to convert Harleys to left-handed throttle and right-tank shift. There were special "reverse spiral" handlebar spirals (the handlebar ends that the rubber handgrips cover) to make the cables push and pull correctly to operate the throttle and spark advance, and special rt. side gas tanks, with cross-over shafts and mirror-image gearshift gates to shift Harleys with the right hand. With these optional features, Harley went after Police Departments used to operating Indians with their now-competitive product, not requiring the retraining of the department's riders to learn the Harley control system. Indian also made all of the parts necessary to shift, clutch and gas an Indian just like a Harley, if the rider preferred, always a consideration when trying to steal loyal customers from one marque to the other.
Rubber = Tire

S-U
Short = Low Final Drive Gear Ratio
Shotgun Pipes = This style of exhaust had the two pipes ending straight and together, giving the appearance of a double barreled shot gun.
Skid Lid = Helmet
Slam or Slammer = Jockey Shift
Sled = Bike
Slider = the throttle throat opening mechanism on a CV carb controlled by a diaphragm & Vacuum.
Slug = Piston
Smell Me Bars = Ape Hangers
SNAFU = After attempting to fix something that wasn't broken in the first place and ya can't put it back together correctly, you have a Situation Normal All F**ked Up
Sneakers = Tires as in "I got a new rear sneaker, or a new pair of sneakers"
Software = What your back warmer presses into your back.
Spark Plugs = Plugs
Spanny = 2-stroke expansion chamber
Sissy Bar = Passenger Backrest, Pussy Bar
Stinky Finger = priming the AMAL carb on early Triumphs from fuel seeping out the button.
Straight Pipes = An exhaust system with no Baffles inside and the exhaust went straight through unrestricted.
Stretch = A chopper term for increasing the neck rake of a motorcycle by extending the length of the frame's front downtubes, which is that part of the frame between the neck and the front motor mounts. Stretching is a chopper modification dating from the 1960's. Its effect was to raise the fork neck, increasing the degree of rake, and allow for the use of a long, extended fork without significantly raising the engine and drivetrain (and bike's center-of-gravity) high into the air. The bike retained a low, long look, high in the center, front to back, and handled relatively well.
Stuck = Sudden Engine Seizure Eg= This also refers to a Stuck Piston which will cause a Gradual Engine Seizure, where the bike will loose power and need to be pulled over to cool-off. i.e. The engine was overheated and/or wasn't broke in properly or the clearances were set wrong and the engine Stuck a Piston. This can happen if the piston to wall clearance is set to close on a forged piston which expands more and faster than a cast piston and can seize the engine when there is no more room/clearance for a forged piston's expansion.
2-1 = 2 exhaust header pipes mating into one pipe
Tall = High Final Drive Gear Ratio
Tampon = Folding a piece of paper towel in the Air cleaner to absorb the breather oil that gets sucked out by the Air Cleaner on Harley-Davidson Evolution engines.
Thumper = Single cylinder 4-cycle motorcycle; vibrates like H***!!Common on dirt bikes and enduros
Tickle the Pot = Tickle is Prime & Pot is Carb. If you have a "kicker" it's necessary to "Tickle the Pot" as the first step in getting a cold engine to start. Refers to old carbs (like Amal) that were primed by a button that pushed down the float and flooded the carb. The old Bing BMW carbs were like that
Tire = Rubber, Sneaker,
Too Late Light = Oil Pressure Warning Light
Trike=A three-wheeled motorcycle. Harley-Davidson's model was the Servi-Car (built from 1929-1973).
Tuppermobile = Any Bike that has plastic arm rests for passengers (like Honda Goldwing)
Turn Signals = Blinkers
Twingle: A vertical twin engine where both pistons move up and down together. combination of the words twin and single.
Twingle (#2) =I hate to be picking the fly shit out of the pepper, but the definition of "twingle" isn't quite right. In all vertical twins, both pistons rise and fall at the same time, so they can fire 360 degrees apart. A "twingle" has a different cam and ignition to make it so both jugs fire together, kind of like a split big single, or a twin single. XR750's are also set up this way sometimes, but they fire 45 degrees apart. Sorry to be so picky, but being an old racer, this one kind of caught my eye.
 

"Uncle Fester" = Somebody who thinks they know how to wrench.
Up-Sweeps = This referred to the style of exhaust that would run up along the side of the bike at an angle often up to the sissy bar or as far as the owner wanted.
 

V-Z
Vermatherm Valve = Temperature adjusted oil pressure control valve used to control hydraulic fan speed.

Wind Shield = Wind Screen
Winkers = "Turn Signal" in Honda manuals in the '70s
WOT = Wide Open Throttle, as in for plug checks of main Carb jetting.
Wrench = Mechanic
Wrenching = Actually doing the maintenance and repair of a motorcycle.

Zorst = Exhaust