As Jim mentioned, the above mentioned plugs are the most commonly used plugs in North America for small, 2stroke engines like these.

Anything in the Champion RCJ?? or RDJ?? series should be fine, or a competitor's equivillant with 14mm threads.

Click on the manufacturer below to interpret their numbering system (from www.sparkplugs.com):
- Champion
- NGK
- Denso
- Splitfire
- Autolite