I’ve seen spark plugs with a cracked insulators and open conductors. But it took me a little while to isolate the problem with my Hitachi gas blower.
Hitachi Gas Blower

I’ve had the blower for several years. It has been a workhorse. It became difficult to start, but once started, it performed as usual. Bad fuel? Time for a new blower?

The problem seemed to get worse over time. During more-than-one troubleshooting session, I repeated the following:

  • Drained the fuel and replaced with fresh mix of fuel and 2-cycle oil.
  • Removed and checked the plug; good spark, no cracks in the insulator, gap as specified.
  • While the plug was out, I checked compression.
  • Visual check of the carburetor and choke; getting fuel into the cylinder.

After reassembly, no change. The frustration continues.

At the beginning of one-more troubleshooting session, after removing the spark plug wire, I glanced at the plug. There was a slight amount of fuel on the insulator and it appeared that the insulator was not perfectly parallel to the base of the plug. The insulator wasn’t loose, just ever-so-slightly off-center. Huh? I remove the plug; still had spark. I blew into the base of the plug; no air passing to the outside of the base. Even though, functionally, it passed all my tests, it was time for a new plug. Cheap fix if it was the source of the problem. New plug, problem solved! (Yeah, I know, I should have just changed the plug at the beginning of the first troubleshooting session, obvious defect or not.)