CrankCase Pressure SPN 101 FMI 15 FC 1974

[Waterloo]

Like I said above, replace the key sensors on the motor, there is a video in the video section of Rawze doing the tuneup to an 871, pretty similar, you have one less sensor, the differential pressure sensor is not on your particular motor, but the intake manifold pressure sensor and Exhaust back [ressure sensor are. If you are working the motor hard, it is best to probably replace the intake sensor twice a year and the back pressure sensor yearly.