Cleaning spark plugs

by Had Robinson
November 16, 2024

Why not get a wire brush and go after the deposits on the spark plug so it will work like new?

Trouble is – that is not what happens.  The best way to clean a spark plug is with a special sand blaster and most home shops do not have one.  When the plug is cleaned with a wire brush (of any metal type) a microscopic layer of metal is deposited all over the plug, including the white insulator near the tip.

The accumulation of anything conductive in that area shorts the plug out.  A sure sign of a fouled/ruined spark plug is to remove the plug, reattach the secondary wire, and spin the engine.  If it is dark enough it is easy to see the spark scatter across the surface of the insulator instead of going to grounded electrode.

Unfortunately, nearly all paramotors have two stroke engines which requires the addition of special oil to the gasoline.  Pure gasoline burns without leaving a residue but this is not so with the burning of the added oil.  When all oils burn they leave an ash residue.  This residue collects on the spark plug and eventually fouls it.  This fouling can be removed with sandblasting.  The plug may otherwise look OK but it is'nt.  This is why the spark plugs in two stroke engines need to be replaced often e.g., every 25 hours or so.

I occasionally see plugs that have been wire-brushed and the pilot wonders why the engine does not run?  The plug below looks perfect but it is fouled from cleaning and is shorted out and useless.

The proper solution is to always buy a new plug.  The only exception might be is if you have a sandblaster and live in a country where sparkplugs are expensive or hard to obtain.  Sandblasting removes the ash and other fouling due to the burning of the oil in the gasoline.  Use a thin file (not sandpaper) to dress the electrodes.  Sharp edges are more effective in igniting the air-fuel mixture.  In the U.S. and some countries, it is not worth the time or effort to clean spark plugs.