I think maybe I was not clear about the problem.

The engine has a CH ignition that they call a T.C.S.A. (Throttle Coupled Spark Advance). There is nothing I have added or adjusted. The engine has worked well for over the 10 or more years ithat I have owned it - until this summer. The module has been upgraded a couple of times during that interval with CH to replacing components and has always run well. I just got the module and sensor back from CH where they refurbished it and tested its operation. I fully expected that this would cure the problems, but alas no.

I took the mechanical advance apart to see if there had been any shift in the magnet position due to a movement of the propeller hub (damage to the keyslot). That all looks fine and everything is free.

It has to be something outside of the ignition and mechanical timing mechanisim.

Last week a fellow at the field had an engine with an optical kill switch that was backfiring through the carb. Taking the kill switch out of the battery feed solved his problem and our best guess was that something in the switch circuit was intermittent and the making and breaking of power was causing the ignition to fire at times other than when the hall effect sensor was near the magnet. None of us knew einough about the ignition circuits to really understand how this could occur.

If the rain stops, I think I will try bypassing the JR charge switch that I use as a kill switch and see if that solves the dilemma. If not I am out of stuff to change unless there is something anyone can think of besides timing that causes this back fire situation.


Thanks for the input.