Lynn,

 

it is a P-Port, which certainly adds to the MAP issue. I am seeing that on the single rotor when the MAP connection is right at the rotor housing, even with a 40thou hole. All I do is showing it on a boost gauge, it is unreadable below 1500RPM.

Fortunately, it is not an issue with a carb.

FWIW.

 

Richard Sohn
N2071U

Perhaps a .020" hole in both ends of the gage line. You have it sitting on a resonant at idle and the gage will go away after just a bit. Like putting a fuel pressure gage too close to the outlet of a sliding vane fuel pump. It just shakes to pieces.

 

With the good breathing required for good power, there will be no manifold pressure (vacuum) until the RPM is close to cruise, And then only if cruise is at a bit less than wide open throttle. Maybe the air filter will provide enough drag to get a reading. In fuel injected systems, the lack of a choke, or venturi just adds to the problem.

 

Lynn E. Hanover