I have a Walker 4.2 engine with a CH Ignition using a mechanical advance that has run correctly but now behaves strangely, and I wonder if anyone has had aimilar issue.

The problem - The engine starts and runs at an idle although it is not quite smooth. If you advance the throttle the engine begins to lose power and runs rough and in most cases will backfire through the carburator sometimes violently enough to kill the engine. Because the engine is firing at the wrong time I am assuming it is an ignition/timing problem.

What I have done is

1. Checked and changed the battery - good and no effect.

2. Returned the ignition module to CH and had an overhaul and check of the module, sensor etc. .................... problem still persists.

3. Dismantled the mechanical advance to insure nothing is loose, unkeyed or misaligned.......... No fault found all seems to work as intended.

Being unfamiliar with the actual circuits of the CDI, does anyone know if I had an intermittent in the battery switch or a wire connection is it possible to fire the ignition at the wrong point in time? This is my latest theory but other ideas are welcome - I am running out of things to change out.

Did you set the total timing at full advance? Should be 28 degrees

The back firing is a sign of advanced timing

Mount a degree wheel and set a reference pointer at zero when the engine is in top dead center.
The spark plug should fire when at 28 degrees before top dead center when the engine is turned over slowly.
When turned over faster, like in flip starting, the ignition will retard to 9 degrees before top dead center.
When rpm reach 2000 - 4000, the ignition will slowly stop all retarding and operate at 28° BTDC again @4000 rpm.

Installed like that should stop all rough running, if the carb is adjusted well and the engine is mechanically ok.

There seems to be confusion as to what has been modified about the engine by the OP?

Was a new CH Synchrospark type variable advance added to the engine?

Did he do away with the original mechanical advance?

Good call. If it now has a SyncroSpark while maintianing the old mechaincal linkage he's going to have problems. If CH did the upgrade there's little reason to suspect that it was not removed.

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.

If it were mine, I would still check that the full advance position was 28 degrees BTDC as described earlier


Go to the CH Site for instructions as how to do this

The problem - The engine starts and runs at an idle although it is not quite smooth. If you advance the throttle the engine begins to lose power and runs rough and in most cases will backfire through the carburator sometimes violently enough to kill the engine. ................................................Ma ybe the carb is set to rich on Idle and is loading up causing your problem...not sure. Capt,n

TCSA timing is 28-30 degrees BTDC at WOT and 4-8 degrees at idle.
Quick and dirty check, AT idle, with the engine at TDC the magnet will be just leaving sensor. Sorta like a figure 8.
Make sure the linkage is going in the correct direction, from idle to WOT the sensor ring moves CW.

You have a carb of fuel delivery problem. Backfiring through the intake (carb) is a tell tell sign that the mixture is lean. The other indication is no problem was found with the ignition. The problem was fuel delivery from the start. Find someone who can disassemble the carb completly (all screens) and put a kit in it or purchase a new carb and your problem will go away.

I disagree. I think the timing ring has moved or the linkage is out of adjustment.

I had exactly the same thing happen to one of my gassers. Turned out the jomar electronic switch for the ignition went bad. Apparently the e switch would only allow enough current through to run the ignition at idle speed. I proved it by taking the switch out of the circuit, then fixed it by replacing the e switch.

Yes, a bad mechanical switch or any other component with high resistance or intermittent contact can cause the same problem. If you have an intermittent connection, the ignition will fire every time the circuit is either broken or made (not sure which). Under that condition the plug will fire with no regard to the crankshaft position.

Jerry

I have had a couple of occasions, where replacing the switch or repairing cables cured erratic running.
Since it was a normal checkup/repair  procedure, timing should not have changed.

Just to keep everyone apprised of how this comes out.

Today I experimented with the intermittent power supply to see if it fires at the application of power or the removal of power it does. From now on I am going to be sure my arm is clear of the prop arc before operating the kill switch.

Then I removed the kill switch thinking that was the only component I had not touched and it still exhibited the same problem.

Here is what I now know - the mechanical linkage is correct and moving the requistie 28 degrees CW, the keyways are all pristine, the battery has been replaced, the ignition has been overhauled and the kill switch has been eliminated. Hmmmmm.

With nothing left to do I opened the H needle 1/2 turn (Ouch) and the backfiring went away. Now the idle is fine but I lose about 200 RPM after a few seconds at WOT where it settles down and still seems a little rough. I now have to agree with Kimhoff's theory since I have eliminated the ignition and opening the H fuel flow up definitely made a positive difference.

I will let you know how this gets resolved.

Thanks for the input Bob

I had similar strange running problems on a G23 modified for EI with a Ridge Machine system. Tried a number of things that did nothing to improve the running. Finally, I changed the spark plug and it solved all the problems. Have you tried that? Good luck.

"I lose about 200 RPM after a few seconds at WOT"

This is normal. It will always be this way