I put a small hose clamp around the spark plug cap. Tightened it around the hex head of the plug. Using 2.4 and DA 85. Problem solved.

I agree that the first step should be to check the plug cap. The second is to replace the servos. The 645 is a pretty rock bottom servo and the internal electronics may not be capable of filtering out what the servo leads are picking up.

Temps recently dropped here so it's been a little cold for me to want to get outside to mess with it but should be able to this weekend with a warmup coming.


Everything on this build is fresh out of the packaging new.

I need to also check the twitch with the aileron supported as well to see what comes of that... but so far I have not seen any twitch with the engine and ignition off. I wouldn't think this is directly vibration... I've seen surfaces vibrate before but you can actually hear the servos actuating and hear them move and they move about 1/4" up and down... 1/2" total deflection.

Agree with this.

I have a Fuji 34. I first set it up with 72 MHz . All the servos jump all around when I did a range check or moved the transmitter away for the plane. I tried everything I knew to get it right but nothing would work. I sent it to C&H Ignition for a new ignition. Everything has been good since.

For a test try wrapping aluminum foil around the spark plug wire and ground it. If it won't run or runs erratic you have a lot of leak.

did you have a C&H ignition originally or did you replace the old ignition with w new C&H ? Thanks God the problem fixed !

I replaced the original Fuji ignition that came with the engine. I though if it would work with foil on the spark wire I would get a braided sleeve. When I put the foil on it it wouldn't even start. Not even a pop out of it. Decided that was enough and got the C&H Ignition.

Sounds like major problem with the high tension lead at the plug as when you added the foil all the power was directed to ground .(direct short.) Other question on the original installation. Did the plug wire have a rubber boot on it ?

It's simple enough to check and see if it's RF noise or vibration. Run the engine with the wing off but the servos plugged in. That will let you see how the aileron servos act with the engine running but without the vibration it causes. If you still get twitching, you'll know it's an RF noise or electrical problem. If it goes away, you'll know the twitching is caused by the vibration.

Good point

Yes it did have a rubber boot.

Oh well since the C&H solved the issue then I guess what your after.... Was just trying to figure out why no spark when the foil over the plug.....it was obviously shorting out the system. What I used to do with older auto ignition systems is run the motor in a complete black dark situation and watch the blue "lightning " were there was Hi voltage leakage and track it down that way.

I popped the hood on my '57 Chevy on dark & rainy night. There was quite a light show surounding the top of the distributor on the back end of that 301 small block

Yes , that was one of the best diagnosis of the older distributor and coil ignitions but not so much with the new electronic stuff today. Gave indications of cracked distributor caps or other high tension problem areas.

Just another way to eliminate vibration as a cause - if you just take the link off, the servo should stop twitching if there is no mechanical load on it.