didn't prime mine..i just scrubbed them w/a scotchbrite pad(wet)then sprayed some carb cleaner on them,and wiped off with a rag..let dry,then used spray engine paint..i sprayed it into the cap until it pooled and then used a tiny and a regular 1/2 inch brush to apply..used 2 coats,and they look glossy and awesome..and they wipe clean easily..looks great and costed less than $10..
