The model 72D A was used by Maytag for the twins. It is identical in appearance to the 72D but the inside diameter of the flywheel is about .140" smaller and the center laminated coil core is about .070 shorter than the 72D. Very annoying again Mr Eisemann! The flywheels and laminated coil cores are not interchangeable but the coil windings are with the model 72D. The part number for the coil windings is H28-015. When testing this coil recall that the secondary(High tension) winding is wound in a loop and does not have a common ground. One must connect one secondary lead to chassis ground and use the ungrounded secondary lead to test for spark on either side. Always have both plug leads connected to plugs or grounded when turning the engine or the coil can be damaged. these coils are difficult to make and spendy. Spark Plug gap is .037" in lieu of the usual .025". More on this one later.
Not much mention of the 72D and 72DA in the Eisemann service literature. More info can be found in the Maytag service literature.
The coils can be annoying and expensive. The best way we know to test is with an actual Eisemann coil tester of the day. It uses 2 spark gaps and pulses the coil primary through a set if points and condenser and measures the current required to get a steady spark at both gaps. If the current to fire both gaps is below the max for that particular coil it is a pass. The converse is true. resistance measurement across the high tension terminals is of limited utility. It will tell if the coil is open(broken) inside and is a dud and will not assess the condition of insulation/leakage inside the coil. Most coils that are not broken will work unless they have moisture inside. Unless the coil is defective it is best to leave it on the poleshoe.
Fortunately the 72D and 72DA both use the same coil,points,condenser and backing plate.
Here is how the coil under test is connected to the Eisemann winding tester. One primary lead (black clip) goes to the coil ground and the other (red clip) connects to the points with a piece of paper between the contacts. Since the magneto has a built in condenser the condenser switch on the lower left of the tester is turned off. The spark gap leads are connected to the plug wires. The knob in the center obscured by the plug wire is adjusted to slowly increase the current till both gaps fire steadily.
The maximum current for the coil stator assembly for the 72D and 72DA is 1.9 Amps
This coil easily fires both gaps at 1.4-1.5 amps and is a definite pass.
The condenser P/N H20-549 can be an issue with these as they like many of the day can develop electrical leakage and cause a wimpy spark. Fortunately Mr. Lawnboy has an excellent remedy. It is the correct capacity, mounts similarly and is readily available from parts jobbers. It fits earlier Lawnboy products and may be known as 31-1800 or 1800 or 677299. This also works with the earlier 72D.