I have had a couple of the bpm7a that did that but mostly no problems. In the NGK I primarily stock the b2lm. bkr5e, bm6a, bm6f, bpm7a, and a few others.
Also because we sell and service redmax equipment their strato charged engines call for NGK spark plug numbers CMR7A and CMR7H. It's good to have a few of each of those.
Edwards Saw Service in Glen Mills PA