Not Your Common Interference Problem
 

I have been frustrated by this problem for some time. When I have my Quadra 42 w/magneto ignition running the servos go wild. At any range when above half throttle. I have changed radio gear to no effect. I shielded the aileron servo leads and have noise traps in the y-harnesses. Other basics are taken care of: no metal pushrods running forward, ball link connector on the throttle, and good separation between the radio gear and engine. Metal-to-metal vibration gremlins checked. I replaced the spark-plug and mag coil w/spark lead in a failed effort to kill the problem.

Yesterday I tested the plane with a different engine (US41 w/CH ignition) and the problem was completely gone. So now I know it is something in the engine rather than a weakness in the radio system. It is also not likely to be vibration related as that has not significantly changed.

This Quadra has been very good and reliable until now. It does have about 200 total hours on it, but I don’t consider that so much. I have run it successfully with an old Futaba 7-GK AM system (now running FM-PPM). I have run it successfully with the throttle servo right behind the firewall (since moved about 14” back). No problems.

What could be the cause of my interference? The complete ignition system is new. The bulk of the other causes I can think of still remain with the aircraft and have been eliminated. What else could be going on in that engine that would light up my radio gear?

I am at a loss.

Bedford

RE: Not Your Common Interference Problem
 

Try wrapping the spark plug lead and the spark plug with aluminum foil. Ground the foil firmly to the engine at the spark plug. If that helps get a Bosch spark plug cover from C&H.
If you replaced the spark plug make sure the sales clerk didn't slip you a non resistor plug.
Take the C&H system off the US41 and try it on the Quadra. If it fixes the problem get rid of the mag

RE: Not Your Common Interference Problem
 

"The complete ignition system is new"

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Did the interference begin after the ignition system was replaced? Or was the replacement an effort to quell the preexisting problem?

Having 200 hours on an engine must make you proud. It would me. However, things do wear and get loose after a while - or could be what's causing the problem. Maybe it isn't. I'll bet you have gone over this engine with a fine tooth comb, but I wonder about such things as the choke plate, or even the carb shafts for the choke and the main throttle plate. Any looseness there? Yes, I'm really stretching, but there must be an answer.

How are the coil mount threads? Any sheet metal in that vicinity that could be vibrating?

Others have already pointed out the ignition ground and plug shielding. This would really make a great follow up thread, if you're in the mood. Good luck.

RE: Not Your Common Interference Problem
 

The following things apply more to older systems but could happen if there is a defect in a new component.
There are a couple of other things that can cause the magneto system to generate interference at the higher speeds.
One is the coil is starting to break down but has not fully failed.
The other is a failing plug wire or boot that breaks down when the cylinder pressure builds at higher speed causing the plug gap resistance to increase which in turn causes leakage thru the wire or boot insulation.
The coils can get noisey when the speed increases and the magneto shoots more voltage to them causing a partial breakdown of the coil insulation.

RE: Not Your Common Interference Problem
 

Believe it or not, I saw a case where bad bearings in the engine caused interference.

RE: Not Your Common Interference Problem
 

The coil and plug were changed to address the problem. So it existed before the change. The plug is confirmed to be correct. I buy my plugs from CH or Bennett and they don't slip anybody the wrong product.

Pile-O-Wood, I have heard that too, but only with regard to helis. I have thought about this possibility, but in all the threads over the past years, I have not heard that suggestion for gassers. Anybody have confirmed experience with engine bearing noise causing the problem?

Thanks everyone for your input.

Bedford

RE: Not Your Common Interference Problem
 

Is the Quadra with the contact breaker ignition like the 34? Then clean up the contact points, and replace the condenser as well.

RE: Not Your Common Interference Problem
 

Did you try what dirtybird said? Wrap the spark plug wire and cap with aluminum foil and ground it to the spark plug. That's the first thing that I would have tried.

RE: Not Your Common Interference Problem
 

had a g26 do the same thing after i changed the pick up. the problem on that was the clearance between the flywheel & the pickup was to close.

RE: Not Your Common Interference Problem
 

Haven't tried the aluminum foil, yet. Will get to it when possible.

For crashhappy: I set the coil gap per spec when I installed the new one. Thanks for the idea, but I don't think that's it.

Bedford

RE: Not Your Common Interference Problem
 

Actually this is a very common thing.... We sell LOTS of the Bosch resistor caps to folks with mag ignition engines.

RE: Not Your Common Interference Problem
 

Thanks, Terry.

Can you descibe the complete installation using the Bosch rsistor cap on a magneto engine. I will get you you soon for a couple and some spark plugs.

Bedford

RE: Not Your Common Interference Problem
 

Remove rubber spark plug cap, install Bosch cap on stock spark plug wire.:D

RE: Not Your Common Interference Problem
 

Thanks!

Bedford