A low cost leak down gauge can be built from two 0-100 gauges, a pressure regulator, and a plug between the gauges with a 0.040" hole. This is what the piston engine aircraft rebuilders use to check leak down.
It can also be used to check manifold leaks by pressurizing the intake. You will need to make a plate to cover the carb side of the manifold and tap for a fitting. Pressurizing the intake and using the leak down gauge will help identify if there is an intake leak and where it is. You will need to remove the rocker arm assembly to make sure all intake valves are closed.
