Hi guys- I'm wondering the results you have of pressure testing a JD? I can't stop the soap bubbling at the intake housing nut area. Thing I don't get tho is the housing is not a sealed fit on its OD into the cylinder. So, any pressure from the intake manifold seems to be able to go "around" the housing, and out past the nut. It is not related to the valve open or closed. Even if the threads of the nut have sealant, the pressure can get over the top of the housing, past the rocker tower base and out. I made the top of the intake housing as flat and smooth as I could, I did the same on the rocker tower bottom and the surface the nut rides on, and I checked the bottom of the nut for flat- I did this using 220 or 320 on a granite plate. I lapped the bottom of the housing to the cylinder.
I don't have any leaks at the intake manifold nuts, etc. But this still seems to be a source of a vacuum leak in operation. But the design to me does not seem to lend itself to being sealed? At least not like a Pan I did where it was obvious at a manifold o ring. When that was fixed, it made sense.