Spark Plug Advice Needed

Dan the man said
Doesn't manifold vacuum drop off as engine speed increases? If this is true then why hook up the vacuum advance to manifold source. If the vacuum drops off as engine speed increases then your vacuum advance isn't even working. If it was me I would do a complete tune up including tuning the carb

When vacuum drops the load goes up. More load needs less timing. Unless it absolutely positively had to have it hook to manifold vacuum I’d hook it to ported vacuum.