NGK BPR6es vs BPR5es

[ripcord]

There usually isn't any adjustment screws on modern equipment and they tend to come a bit on the lean side for emissions. The problem with that is the least bit of junk or varnish clogging the carb puts it over the top. To enrich, I would first clean the carb. If that didn't work and I had eliminated everything else drilling out the jet a tiny amount.

I would check the valve lash fist, myself. Also, a partly plugged fuel filter can cause lean running, too.

 

[Cujet]

That will explain this.


View attachment 43079

That's probably the catalytic converter, properly glowing. A colder spark plug will not change that.

The colder heat range spark plug will itself run a touch cooler, not the engine.

 

[ragtoplvr]

It is normal for a air cooled engine worked hard to have a glowing muffler. The old flat heads even had flame coming out of them under heavy load. The OHV engines burn better, but the muffler will still glow, best seen at dark. Even my cub cadet kohler, I added lights and mow after dark in the hot summer. The bigger muffler on it will glow to a dull red.

Does not seem to hurt the engine.

 

[Alain2]

I have the same washer and checked the plug, it has a #6 from new.