Manifold Pressure problem

[Jerry De Santis]

My plane is a P337G 1975 model with Riley A.C. and Intercoolers. Engines are TSIO-360 CB's

Problem: Rear engine manifold pressure does not go lower than 24 inches. We know it is not the gauge because we switch connections from rear engine gauge to front engine gauge and the problem stayed with the engine.

We disconnected the line from the gauge and the hoses on the rear fire wall and blew air through it to make sure nothing is impeding the line. It is clear.

Anyone have a suggest where I should look next to determine the problem?

Cheers
Jerry
N34EC