Re: Rich running after warmup

There are two external mixture control devices that are in play. (External to the fuel distributor [FD], that is.)

1) The warmup regulator [WUR], which contains a heating coil, that if not functioning, will cause the WUR to remain in the rich control mode. The WUR also contains a manifold absolute pressure [MAP] sensor. If the vacuum line to the MAP is leaking, or the seal of the MAP section of the WUR is leaking to atmosphere, the mixture will be rich.

2) The frequency valve, which is controlled by the O2 sensor in the exhaust, and the electronic control unit that processes the O2 sensor signal, and thereby controls the frequency valve. If the O2 sensor is defective, its control unit will keep the frequency valve in the default mode, which is somewhat rich.