Glad to hear that you got the engine to run! Progress!
Sparking from the brushes and commutator is normal. Make sure the commutator, brushes, brush springs and brush holder are all cleaned with naphtha. Worn brushes (very short) should be replaced.

Now to the e-unit.
Some e-units buzz more than others, and there is really nothing that can be done to lessen it. It is just a product of manufacturing tolerances.
Remove the e-unit screw holding it in place, and remove the e-unit. Inspect it carefully. Look at the rotating drum and the 2 sets of contact 'fingers'. If the drum and contacts are dirty, get some plastic compatible spray contact cleaner and spray the contacts and drum. Lift the plunger and pawl by hand to cycle the e-unit manually. Inspect the drum and note the copper contacts on it. Watch how the 'fingers' make contact with the various segments of the drum as it turns. Make sure all the 'fingers' are straight and have proper tension on the drum. Look at the ends of the 'fingers where they contact the drum. Look for dirt, grease, and even holes in them from wear and arcing.

Any problems with either the drum or finger contacts will require dis-assembling of the e-unit for service. Servicing the e-unit is not for the faint of heart and is what separates the men from the boys. It takes a lot of patience and 3 hands to properly reassemble an e-unit.

Here is a 2 part video of an e-unit being serviced to give you an idea of what needs to be done and how to accomplish it. If you are confident in your skills, go ahead and service the unit. If not, a Service Center will repair it for you, or an option is to replace it with a new unit.





Larry