I have used it without a sealer & had no issues..
here's a list of the primers for Hawkeye Industries website.. You will still need to sand the surfacing primer with fine paper & buff, it has the...
My money's on an "Intake Leak"...It happens alot.. Are you useing the rubber end gaskets supplied in the gasket set... If so, that's the...
I use Duratec Surfacing Primer on plugs as it produces a harder, glossier finish than sanding primer.. Sanding Primer is OK to buildup a surface...