I found this,
Rotax spark plug advisory for ultralight, experimental lightsport, amateur built aircraft. Rotax 2 stroke aircraft engine spark plugsThe recommended spark plugs for the Rotax 277, Rotax 377, Rotax 447, Rotax 503, Rotax 532, Rotax 582 are the NGK B8ES series or the NGK BR8ES ( the R in the spark plug denotes it is a resistor plug and should be used in all of the CDI ignition engines.
BUT the Bosch points ignition engines should NOT use both a resistor plug and a resistor spark plug cap - use one or the other.
The least expensive option in the long run is the cap as you purchase it once while the resistor plugs cost more than the standard plug each time you buy them.
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Use spark plugs that have a SOLID TIP - DO NOT USE spark plugs that have an aluminum screw on tip. They vibrate loose, the tip wears making a loose cap to plug fit, and can lead to the spark plug arcking across from the cap to the plug. Also the screw on style spark plugs are NOT designed for our applications, the gap is generally set up for .030 to .035 thou. The solid tip spark plugs are set up for a gap of .015 to .020 thou. Spark plug gap
- Allowable range: 0.4-0.5mm / .015 -.020"
- Optimal: I usually set them to .015 and let them wear out to .019
- This also helps getting the engine started in colder conditions
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