I pay the price getting cold by examine the bike over 2 hrs in the heavy rain that day and just now I spray water directly into the spark plug area for like few mins but no luck to re-create the stutter and stop issue, may be the "free the water from the bottom bowl of the carburetor" trick that foreman show me really work ??   


Regardless I will definitely change my plug coil / plug lead / cap altogether because many people or google search mention it do bring back a good amount of engine performance in whatever condition after the old one already use for so long.

thanks for doing this
we ruled out the plug cap

next is possibly the carb is leaking water, or the air intake is ingesting water

Regardless I still plan to change it consider my bike already 10 yrs old and I still need another 1 or 2 at least 30mins heavy rain session to confirm the stutter and stop issue are really gone.

By the way consider my Air filter has no foam inside for god know how long so there definitely a good route for the wet air to get inside the carb ...

if it's not broken just leave it as is
replace the foam filter. make sure to oil it before install

Yeah I just put in a new sponge, the original one already turn into ash by heat after decade without any proper service. As a matter of fact I don't even know there is a air filter to begin with until 2 weeks ago.

By the way you mean oil the sponge first before install ?? Why ??