The FM-XD1B7 is a single cylinder special flange mounted device used extensively by Wisconsin Motors . It bears a lot of similarities to is predecessor, the FMJ series but uses a different breaker and a vent. This is a reliable and serviceable magneto that is robustly designed like the Wisconsin engines. Here is some service information to keep yours on line by kind permission from Fairbanks-Morse.
The first step before a frontal assault on the magneto is to test the spark as described above. The most difficult and costly repairs to make are those to a device not needing them. Many causes of ignition failure can be traced to improper plugs and wires (resistor plugs and wires are a big NO NO and can damage the coil). Some modern sparkplugs do not have a glazed center insulator that when used with modern E10 fuels can foul easily and not fire. We have used an Autolite 386 with good results. For more info on wires and connectors please see Plug and Wire RX. It is helpful to apply an anti seize agent to the threads.
Check the condenser for leakage, then capacity. it should come in around 0.2MFD. Not to much condenser trouble with these. A condenser for a Delco distributor will work fine. If the points still have meat(Contact material) on them by all means use them. Use a diamond file or stone to get the jagged edges off the polish to a mirror finish and they will stay clean. Make sure that the contact surfaces line up with each other when closed. Bend the stationary point as needed and/or add a spacer to the breaker lever shaft. If polishing the points shows a reddish copper like tinge, the contact material is gone and the points need replacing. When testing the coil, best to remove it from the housing as when pulsing the coil with the tester, it may discharge the magnets in the rotor. Be mindfull when removing the two 1/4-20 slotted setscrews holding the coil in place. They are very hard, brittle and one side of the slot can break off causing discouraging words and a trip to the milling machine for a Helicoil insert. Use a good fitting screwdriver and if the screws do not come out easily, heat the top of the housing with a propane torch. Sometimes the screws have a heat sensitive thread retainer that will let go and the heat will make the housing grow bigger than the screw. It is not usually possible to tell by looking at the coil or using an ohmmeter to see if it is good or not. Use an actual coil tester for a valid test.
The coils (part# S2477C) used by these magnetos look like those used by the multi cylinder counterparts but are coloured black and made different. I do not know all the answeres to this issue.