how do you know what kind of spark plug goes in which moped and how to gap it? what does gapping mean? does it have to be perfectly gapped?
Re: spark plugs?
A manual will tell you the type of plug to use and the proper gap.
If you can't buy the recommended brand, Plug numbers are standardized and all the different plug brand names can be cross referenced for substitution.
The differences in plugs are the length of the threaded part and it's diameter, how quickly that plug absorbs heat, electrode design and a few other things. Although most 50cc 2-strokes use only a few very similar plugs it's best to get the one recommended for your engine.
The gap is the distance between the center electrode (round.. sticks out of the middle) and the ground electrode (flat.. attached to the edge.) The flat one can be gently bent out or in to adjust the gap. A autoparts store will have a gapping tool that includes little wire gauges and a tiny "wrench" thing to bend the electrode.
Electricity easily sparks across a small gap but the spark doesn't last long and is weak. Also, a tiny drop of water or oil can 'bridge' that small gap and cause a misfire.
Wide gaps provide a longer spark that also lasts longer. However it takes more energy to spark across a wide gap and a weak ignition pulse might not make it, causing a misfire.
So, accurate gapping (adjusting the distance between the two electrodes) is important. Get a good sparkplug gapping tool.. i guess they are about $3 for a cheap one and maybe $6 for a good one.
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