I should ask this of C&H but they are very busy this time of the year.
I have a C&H Syncrospark unit that came with a shielded spark plug lead for use witha 1/4x32 plug. I flew the ignition for several years on a G45 but the plug lead eventually broke(I used an adapter in the engine to fit the small plug). I replaced the plug lead with non shielded solid wire lead and a 14 mm NGK cap with a built in 5K resistor. I also installed a resistor spark plug.
I also grounded the ignition case with a pigtail from its case to the engine.
The engine runs fine but it wipes out the radio.
Is there something about the C&H syncrospark unit that makes it unsuitable for use with an unshielded system?

You are probably picking up spurious "RF" emissions from the unshielded wire. I'd call call C&H for their recommendations, or ask Ralph, at rcign.

unshield setups - really not modern idea -- the ignition case must be grounded to the base of the plug (thru the head via a ground lead from case of ignition ) but you have effectively increased the paths of any radiated crap (engineering term.)
Terry at CH will likely tell you something similar -

I guess what you are telling me is a shielded lead is needed up to the plug and a pigtail that is clamped to the base of the spark plug. At least that is how my BME 100 has it. Then the shield provides the ground and the case pigtail is unnessary.
What I don't understand is how a mag system gets away with a completely unshielded system

mag is grounded directly to case/head.
shorter path.
I had a friend (Al Diem) make up some special ignitions I used - extremely short plug to coil - then, a remote CD setup (In shrink tubing) to the coil. so the total loop of HV was about 4". (coil to plug to head to coil) I used a small plug in a ST2300 on alky n a splash of nitro . better than any of the so called perfect Pattern engines I see. smooth as glass and 9000 on 18x8 APC
still------ too expensive to feed.

I wrapped the entire spark plug lead in aluminum foil and connected it to the ignition case and put a pigtail to the spark plug. It helped but it still was unsatisfactory. I guess I will have to send the unit back to c&h and have them fix it

Just send it back to C&H and have it repaired. not worth all the hassle.

Why not use a section of coax for your plug lead and let us know how it works. Extend the coax shield to engine ground at the plug. Good luck, red

Whats your plane worth??? A new cap and lead fron us is about $30 installed. Notice everybody is suggestion expermentation on your palne.

Not everybody-- for $30.00 a properly installed HV lead is a good deal -

Generally my airplanes are not worth $30. I don't intend to fly it anyway until its right. It might hit someone.
I am thinking I might just pop for a new one set up for my engine.
Question:
Since I use a Miller starter and never prop by hand not even on my 100, I won't need the Syncrospark unit. Right?

I tried coax once. I couldn't get it to work. I didn't try very hard though.

I would opt for the SynchroSpark - the overall smoothness at idle is better .
I hand prop everything -but all my ignitions are at zero advance whilst starting - No flipping - just easy pull thru.

Excuse me but, my suggestion was to send it back to you for repair. Bob