# What should outboard spark plugs look like?

A normal spark plug will appear dry with a grayish color. A wet spark plug can indicate water in the fuel while a white residue on the plug can point to a plug that is too hot. If the plug is black with soot, it can mean that the fuel has too much oil while an eroded plug can indicate a too-hot plug.

## Are spark plugs constantly firing?

A narrow gap may give too small and weak a spark to effectively ignite the fuel-air mixture, but the plug will almost always fire on each cycle. A gap that is too wide might prevent a spark from firing at all or may misfire at high speeds, but will usually have a spark that is strong for a clean burn.

## How fast do pistons move in an engine?

For example, a piston in an automobile engine which has a stroke of 90 mm will have a mean speed at 3000 rpm of 2 * (90 / 1000) * 3000 / 60 = 9 m/s.

## How many times does the crankshaft rotate in a 4 stroke cycle?

A 4-stroke engine fires once every second rotation of the crankshaft (every fourth stroke of the piston).

## How many times in a 4 stroke engine does the spark plug fire?

The common challenge is to understand that these 4 cycle engines actually spark twice (not once) during the 4 strokes. One spark comes at the end of the compression stroke and another (wasted) spark comes at the end of the exhaust cycle.

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