OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Honda Engines Yard King 125cc Briggs 450-series which spark plug?

the reason I was forced to keep exploring the issue, is that although that old needle-pointed NGK seemed to cure all ills and thing ran like Swiss watch with it initially, it did not last...began sputtering Thursday shortly after starting on front yard ...conked out altogether, and that conk-out and re-start attempt met with half-baked backfire back though carb/air cleaner even..

tried fresh used plug cleaned with wire brush...re-started, ran ok but not perfectly..

engine appears to have some plug-fouling issue...but I'm not sure source of fouling, rich mixture soot or oil and burned oil...or maybe some of both..

I do sort of get a vibe that thing runs a little rich for whatever reason..

G'day BriggsHandy,

I don't know how many years old this mower is, but the rings may be worn and it's burning a little oil ,if so you would
install a a spark plug with a hotter heat range, example if your current plug is a champion RC12YC, you might switch to RC14YC.

The first thing to check with a plug fouling issue is a dirty air filter as that causes over fueling.
Incorrect valve clearance can contribute to spark plug fouling and various engine performance issues.

While increasing the heat range of the spark plug can help with fouling, it's essential to diagnose underlying issues contributing to the fouling first. If switching to a hotter plug does not resolve the problem, more investigation may be necessary to fix the root cause of the fouling.

The spark could be a little weak indicating the coil needs replacing ,I had one the other day that wouldn't start ,I didn't check
the coil, I just replaced it with a second hand coil and it started straight away.

I've had problems when buying new coils online that don't work so I prefer to get a new genuine coil or just use a good second hand coil.

Cheers
Max.