1. mercury
   carbon dioxide
2. ash

Less ash makes burning the oil a little bit cleaner.

1. two
   four
2. five

Hence the name.

1. six
   four
2. one

The crankshaft makes one complete turn.

1. bluish
   grayish
2. white

It gets its blue tint from the oil that's blended into the fuel.

1. 1781
   1881
2. 1913

Dugald Clerk invented it in Scotland and patented his creation in England in 1881.

1. self-oil using a discrete oil tank
   self-correct for vibration from the pistons
2. combine compression with ignition

It combined compression with ignition during each revolution. Clerk succeeded where other inventors had already failed.

1. longer lives
   a good power-to-weight ratio
2. better functionality

They're often used in small power tools and light vehicles because of their power-to-weight ratio.

1. open
   closed
2. partially closed

They are both open. Air pressure differences cause a fresh fuel/air mix to move into the combustion chamber.

1. Wilhelm Maybach
   Sylvester Roper
2. Alfred Scott

Scott also had about 50 other patents to his name.

1. kerosene
   petroil
2. gas

Petroil, or two-stroke oil mixed with gasoline, makes the total-loss oiling system work

1. far fewer parts
   far more parts
2. about the same number of parts

The lower number of parts in a two-stroke engine is the primary reason they tend to be lighter.

1. 2-to-1
   6-to-1
2. 10-to-1

The 6-1 ratio is fairly low for small engines.

1. 12-to-1
   16-to-1
2. 20-to-1

The typical compression ratio is 12-to-1. Higher compression ratios generally mean more power.

1. three times
   twice
2. once

It only fires once per revolution. This trait helps two-stroke engines produce more power, by weight, than four-stroke engines.

1. spark ignition
   electronic ignition
2. neither

Gasoline ignition is especially common in the smallest two-stroke engines.

1. true
2. false

Staying on top of lubrication is especially important in two-stroke engines.

1. It makes asymmetrical engine timing possible.
   It lowers noise levels.
2. It improves lubrication.

Asymmetrical engine timing often results in better power output.

1. They are the same.
   Two-stroke engines are a little cleaner.
2. Two-stroke engines emit dirtier exhaust.

The emissions are higher in large part due to the oil that's mixed with the gasoline.

1. two-cycle oil
   two-piston oil
2. two-inlet oil

Two-cycle oil is used in many small engines, from boat motors to chainsaws.

1. It uses extra cylinders.
   It uses direct fuel injection.
2. It has a new ignition technology.

The point of the direct fuel injection is to reduce the amount of unburned fuel in the emissions, making them cleaner.

1. rotary
   reed
2. piston-controlled

The 1970s saw significant improvements in piston-controlled inlet ports.

1. 2 ounces (57 grams)
   4 ounces
2. 8 ounces

You need 4 ounces of oil per gallon of gas, and it can be pricey, too.

1. They are very similar.
   They are completely different.
2. As with smaller two-stroke engines, you're required to add oil to the fuel.

The oil-fuel mixing process is mainly for smaller and cheaper two-stroke engines.

1. true
2. false

Their inefficient oiling methods mean less effective lubrication shorter engine life

1. exhaust
   compression
2. combustion

The upward stroke is the compression stroke, and the downward stroke is called the power stroke.

1. oil leakage
   coolant leakages
2. Friction problems mean higher emissions.

They leave clouds of smoke and trails of oil in the water.

1. oil sump
   carburetor
2. neither

The oil originates in the carburetor. It is mixed directly into the fuel.

1. true
2. false

Two-stroke engines aren't really fuel efficient.

1. They are far less efficient.
   They are far more efficient.
2. They are about the same.

It seems bigger is better when it comes to the efficiency of two-stroke engines.

1. It is very narrow.
   It is very wide.
2. It is the same as any other motorcycle.

Peak power on these bikes occurs in a very limited range.