Several different plugs will work in that engine. I prefer the BPMR6F that TxDiveBomber listed as it is the smaller 5/8" tapered seat plug. Most of these engines came with larger, washered, 3/4" plugs but the numbers are not handy right now. The choice kinda depends on what ignition you are using on the engine. If you have metal capped plug leads, you have to match the plug size to the cap size. If using the black rubber boots on the plug leads, you can use either size plug. Since switching from Champion to the NGK plug, I have never looked back!