I assume you mean the top of the sparkplugis snapped off and the base including the Edges which would engage withspark plug socket are still available. Remove any excess snapped off pieces very carefully. Once done remove using spark plug tool. If you mean that the only thing still sticking out is the top of the base of the Spark Plug then carefully determine which tool wiil best remove remaining piece. Pay particular caution to not damaging spark plug intstallationgrooves(Threading). You may have to use Vise Grips or an easy out or a reverse threaded drill bit. Do not damage threads under any circumstances. If you have to Remove your Tank to gain proper accees this is preferable to damaging the threads. Think it thru first prior to trying anything. The least preferable option will be removing the head, but this is still better than damaging the threads in the head.
Answers & Comments
I assume you mean the top of the sparkplugis snapped off and the base including the Edges which would engage withspark plug socket are still available. Remove any excess snapped off pieces very carefully. Once done remove using spark plug tool. If you mean that the only thing still sticking out is the top of the base of the Spark Plug then carefully determine which tool wiil best remove remaining piece. Pay particular caution to not damaging spark plug intstallationgrooves(Threading). You may have to use Vise Grips or an easy out or a reverse threaded drill bit. Do not damage threads under any circumstances. If you have to Remove your Tank to gain proper accees this is preferable to damaging the threads. Think it thru first prior to trying anything. The least preferable option will be removing the head, but this is still better than damaging the threads in the head.