Originally Posted by
1967brutus
Yup... a leak in the general area of the intake seat, be that a leaking valve or a leaking seat, will strongly affect the required needle settings for a good idle mixture and also affect the ability to "draw" fuel at idle.
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.