We had the same problem recently, initially looking at the mag switch as the culprit. Rather than going through the motions of replacing the switch we disconnected both ground wires and used jumper cables to ground the individual mags on run up. Interestingly the rough running only happened at the 1700 rpm range, and purely by a fluke, the rough running went away when adding carb heat. The problem obviously was not electrical but air/fuel supply, and in this case was the mixture setting on the Stromburg carburator.
John H. ----- Original Message ----- From: Kevin To: [email protected] Sent: Monday, November 09, 2009 8:43 AM Subject: [ercoupe-tech] Re: intermittently bad run-ups I would see if I could borrow a good mag switch and try that. Kevin1 --- In [email protected], Hartmut Beil <hb...@...> wrote: > > > Ed. > > > Excellent analysis. > > > > Running lean can be a cause for that kin of trouble. > > Under lean condition, the effects get worse when only one spark plug is firing in a cylinder. > > > > The quick test is to pull carburetor heat and see if the symptoms smooth out or disappear. > > > > A lean condition can be caused by the carburetor itself but also any intake leak along the way to the cylinders. > > > > > > Hartmut > > > > > > > > > > > > > >
