Hello all,
At my wits end with problem, i have a CMP Giles fitted with an RCS140 gas engine, the only reason i have not flown is i cannot get rid of interference problems when the engine is running. The RX, battery and servos are all as far away from the engine as i can possibly get them, the throttle servo is the closest and that is out of neccecity, i am using a PPM receiver to proof the system prior to install a PCM RX.
The issue seems to come from the spark cap, i have tried two types, both the original, and a DA cap, both present the same problem. Today while i was testing the plane, i held onto the plug cap, so that it was hard against the engine, the interference stopped, release the cap and it would start again. I have come to the conclusion that the issue is spark cap related. Neither cap is resistive and i dont beleive the NGK CM-6 is resistive, could this be the cause. The DA cap is almost new and was bought specifically to test for this problem, it has not helped, although it does sit well on the original lead with the braiding. Futhermore i have also tried a seperate ignition system from a different engine.
Any ideas would be greatly appreciated, i am at my wits end. Can anybody recomend a solution?

The CM-6 plug is not resistive. You will need a fully shielded system. When you hold your hand on the plug cap the problem goes away proves that the cap is simply not making proper contact with spark plug.
My 140 came with a small hose clamp to put around the cap at the base of the plug to hold the cap firmly in place. It needed that clamp.

The DA cap has a resistor in it...
The RCS cap I had here was made by putting a tin shield around an NGK bakelite cap, also has a resistor in it....

Why don't you give Stuart Mackay a ring. I assume the RCS 140 is Stuarts 24cc in the UK.
Colin

Thanks for the suggestion, hopefully will get the operertunity for trying this out today.

Also thanks for clearing up about the resistors, i had a look at the DA cap again, and sure enough there is one in there, dont know what has happened to the original cap at the moment[>:]

Well did not get out to try the clamp today, should be able to give it a try on Wednesday.

If you're using the small aluminum cap on a CM-6 type of plug without a clamp, then RF issues will be probable. Just about everyone using this cap uses some type of clamp to prevent it from bopping aound. Hose clamps are pretty standard.

The aluminum cap, yes...The steel cap on the DA and 3W wires almost takes a screwdriver to get it off...No need for a clamp on those...
The steel cap on the Falkon ignitions I have here is looser, a clamp would be a good idea on those...
If someone is going to copy a cap, why not do it right ?
I haven't seen a Chinese cap here, but it looks like they need a clamp too...

DA adapted to Falkon worked perfectly right from the get go