Re: PACKARD 160 TUNE-UP DATA

Posted by Owen_Dyneto On 2020/7/27 14:13:10

Your vacuum reading is modestly low, is it steady or also fluctuating? If steady it may just be a reflection of improperly adjusted idle mixtures or ignition timing. Old Motors Manuals have a good section on diagnosing vacuum readings. Large rapid fluctuations can indicate valve seating issues.

Your engine if in good tune and internal condition should give a steady manifold vacuum reading at idle of 18 - 20". Under heavy load as in accelerating it will drop dramatically, and upon recovery as in coasting it will rise well above 20".

The figures you provide give the number of degrees of timing change that those various amounts of vacuum provided to the vacuum diaphragm should produce. The vacuum units can be adjusted if necessary to match those values by springs and shims bearing internally against the rubber diaphragm. Best done on a distributor test machine such as those made by Sun.

You check the timing at idle speed and as I noted to you in your inquiry on the Packard Club forum, the idle speed must be below the speed at which the centrifugal spark advance initiates, in other words less than 500 rpm. Nice idle speeds for those motors are in the range 425 rpm.

The vacuum line to the carburetor is ported into the carb bore above the closed throttle plate position. Therefore there is no vacuum present in the line or diaphragm at idle and hence no reason to disconnect it to set the timing. If the vacuum line entered the carburetor bore below the throttle plate, then the opposite would be the case.