Rough running on primary (Magnetron) ignition

[bvolcko38]

The primary ignition runs rough. Secondary smooth as silk. I thought it might be a sparkplug problem, so I installed new top plugs. Both front plugs were black with soot and both rear plugs were clean. The front plugs fire off the top coil. Is it possible that coil is weak? The engine doesn't skip, it is just rough. I started the engine, cold, on just the primary ignition. ran it for a few minutes and checked the exhaust headers, they were all 4 pretty much equally hot .
Is there a way to check the coils with an ohmmeter? I understand these are Briggs and Stratton pn 394891


Any ideas?
Frustration is setting in.

BV

[kmacht]

How many hours on the engine and did it just suddenly show up or has it been a gradual increase in roughness?

Keith
#554

[mike.smith]

Is this a new engine or has it been running for a while? I stupidly had my flywheel magnet installed backward and got the same symptoms you are describing. But if you've been running your engine for a while then that wouldn't be the problem.

[bvolcko38]

Brand new engine. First flight last week

[sonex1374]

Bill,

Check out the gap between the magnatron unit and the flywheel trigger magnet. Also verify that the magnet is oriented properly. It can be confusing, so follow the instructions carefully. If neither of those things show any problems, you might check over the spark plug wires and tips/boots to see any trouble spots. You could have some slight damage to the wires or deformed tips that have gone un-noticed.

Black plugs are common early on while you get the carb tuning perfected, and you should plan on leaning the mixture "brutally lean" on the ground to keep things clean inside. Sooty plugs might cause rough running, but are not necessarily a problem.

Jeff

[kmacht]

If you don't already and the other suggestions dont work, run individual ground wires between the engine and each magneteon. The red annodize can sometimes cause a bad connection and weak ground.

Keith
#554

[Sonex1517]

One other idea to add. I had a plug lead melt against a head and cause this exact behavior on my third test flight.

[bvolcko38]

Will definitely run separate ground wires to magnetrons. And will check magnet polarity. All else seems good Sometimes worse than others 5 flights so far,,,, takes time tosort these things out I guess.
BV

[lutorm]

Any ideas?

Do you have 4 EGTs? It makes troubleshooting things like this infinitely easier.

[bvolcko38]

Yes 4 egts