Originally Posted by Glowgeek

For sure, even worse if the casting void exits to the atmosphere, as it did on my friends Saito. His engine had a casting void from the intake port into the rocker box area. The thing would run different with the rocker cover on vs off. We pulled a mild vacuum on the intake port with a hand pump and drew in slightly thinned JBweld. I worked but I've lost track of him, probably still runs fine.