Weird Spark Issue

After weeks of tracking down some issues I finally made some progress. I got the 72 commando running and idling fine, just have lack of power on takeoff and acceleration. I tracked it down to the left cylinder nor firing, lots of good spark, plenty of fuel, new plugs, no combustion. I can feel the exhaust and it is cold, right side is good. I then noticed that when I take the plug wire off the left side and just rest it on the tip of the plug (not press it on) it will fire fine on both cylinders, I decided to reset the timing (w/ boyer) and see if that is the problem. I then started it up and it fired on both cylinders. there was some popping an spitting so I adjusted the timing a small amount and then I had the exact same issue as before only now it is on the opposite side. (left side good, right side no fire) and same issue w/ plug wire. I undo the small change in the timing I made and still nothing. I have changed the plug, wire, and coil on the side that won't fire with the wire on the plug with no luck. Any idea what may be going on? Could it be a bad ground somewhere?

Do you have resistor spark plugs and resistor plug caps and resistor HT wire? Try swapping one or two for non resistor units if this is the case. Most electronic ignition requires some resistance in the system but too much could cause this problem

Are you running electronic ignition with 12 volt coils? They run much better with 2 6volt coils as they are wired in series.

Good luck with this.

I am running non resister plugs and wires. I have the dual 6V coil setup w/ boyer and podtronics. I have swapped between resistor and no resistor plugs. I have even put on the original Champion plugs and wires w/ original Lucas coils. I seem to have the same issue with all the setups I try.

Do you have at least 10 plus volts in your battery? Boyers are sensitive to low voltage.

Try increasing your plug gap a bit, when you lift the cap off the plug you are effectively making the ignition work a little harder, which sometimes helps. I seem to recall that a number (or all) of the electronic systems specify a resistance in the HT system.

You could also try resistor plug caps, although the resistor plugs you already tried should have the same effect.

dave M said:

I seem to recall that a number (or all) of the electronic systems specify a resistance in the HT system.

Click to expand...

Digital ignition systems normally do, but analog/ue ignitions such as the Boyer Micro MkIII & MkIV don't.

Most boyer problems are due to low voltage cuased by ( as mentioned) poor battery, corroded connectors, dodgy kill switch etc etc.

Just another thing to check.
I had a problem with the boyer wires from the pickup to the bullet connectors, externally they looked fine but the copper wire inside the vinyl insulation was broken.

Easiest way to check boyah trigger leads is with key on and flick at em listening watching for a spark with a plug on head surface and all bets off till those are upgraded replaced as will get you at some point.

As pommie john says, the kill switch is often a culprit as the fed to the ignition has to go through it before reaching the coil and the points get corroded, simply run a wire from the battery direct to the ignition system to check this.

I always use the kill switch to trigger a relay rather them rely on getting the full 12 volts through it.

I changed the plugs again cleaned the kill switch still no change. was about to give up for the day and thought I would increase the gap on the plug (about double) and it started to fire. I went for a ride and had all the acceloration back. After about 20 min it started to sputter and loss of volts from the batterie and stalled. I got it home and checked w/ multi meter and was just over 10 volts. got it running and checked again and was down to 7 to 8 ish volts w/ no change when revving to 4500 RPM, turned it off and was back to 10 volts. I just put in a new batterie, rotor and alternator this year (new wire harness last year) because of the same issue w/ the batterie last year. Guess that wasn't the problem and I am back to tracking down some mystery electrical demons.

Ugh another Commando cliff hanger episode waiting in suspense for a rescue in nic of time. Then again some of us are just not Commando material.

blipJC said:

I changed the plugs again cleaned the kill switch still no change. was about to give up for the day and thought I would increase the gap on the plug (about double) and it started to fire. I went for a ride and had all the acceloration back. After about 20 min it started to sputter and loss of volts from the batterie and stalled. I got it home and checked w/ multi meter and was just over 10 volts. got it running and checked again and was down to 7 to 8 ish volts w/ no change when revving to 4500 RPM, turned it off and was back to 10 volts. I just put in a new batterie, rotor and alternator this year (new wire harness last year) because of the same issue w/ the batterie last year. Guess that wasn't the problem and I am back to tracking down some mystery electrical demons.

Click to expand...

Check all charging system wiring and if all is well there it might be the zener diode shorted to ground ....Try unhooking brown/blue wire from zener and check voltage at battery...If it shows over 12v now the zener is bad....Replace the Zener diode and rectifier with a Podtronics regulator

Well,.... with mechanical ignitions you can be pretty sure if you can have a single cylinder misfire that it can be diagnosed by switching components from one cylinder to the other and observe if the misfire also switches cylinders. I'm not so sure that's always the case with electronic ignitions. (I'm sure someone will comment on this)

My single cylinder misfire turned out to be a spark plug that would spark when held against the head, but not spark when threaded into the bike when under compression. I was so convinced that it had to be good since it tested fine outside the cylinder that it took me many days to figure out the plug was the problem. I figured it out because I started swapping parts from one side to the other. When the miss switched sides with the plug switch, it hit me like a ton of bricks. With new plugs, the bike started on the third kick... with both exhaust pipes getting hot... and I was on to the next tuning issue.

One of the things I had an issue with was a poorly centered stator. The rotor would rub it at certain RPM's and short out the bike. I fixed that by grinding the mounting holes in the stator so I could shift it to be better centered. That year I also rebuilt the bike with superblends. Maybe new bearings helped too. Check you rotor/stator gap. Slowly roll the bike over and see if the gap is maintained.

One of the things I did to insure less chance of an ignition miss, was add a few extra grounds from the engine to the frame. On an isolastic engine, redundant grounding is a good idea....

Lastly, if you have another electronic ignition, you should try and swap it and see if the electronics are the issue. I am currently running a boyer microdigital, (red box) but still have the original black box boyer as a working back up when I upgraded. Having the second ignition module would be a way to eliminate the boyer as the issue.... At some point when the issue doesn't seem to be narrowing itself down, you have to be methodical and start the process of elimination where ever you can.

Another thing can be a dropped carb needle. maybe the circlip popped loose and you're only getting an idle circuit's amount of flow with the carb needle stuck in the bottom of the jet. eliminate gas starvation as a source of the issue by squirting a bit of gas into the carb with the slide up. If it trys to fire when you kick it then dies, maybe your issue is fuel, not ignition...

Believe me, I've had my own mysterious issues to overcome that seem obvious now in hindsight, but were hard to diagnose at the time they were happening.. HTH...

At some point when you are feeling bamboozled, write down all the things you can think of that might cause the issue, then go through your list and test each one. If that doesn't work, then you are down to the basics....

Maybe you threw a pushrod and the valve isn't opening...

You need air, fuel, a timed spark, and compression...

Hi,
May be your left spark plug dont fire because is too much wet, too much benz from the carb.
So the left spark plug goes in "dispersione" (italan word that i cannot able to translate) and do not fire anymore.
Check the correct level of the left float in the carb bowl.
I had the same problem, solved in this way.
Ciao
Piero

blipJC said:

After weeks of tracking down some issues I finally made some progress. I got the 72 commando running and idling fine, just have lack of power on takeoff and acceleration. I tracked it down to the left cylinder nor firing, lots of good spark, plenty of fuel, new plugs, no combustion. I can feel the exhaust and it is cold, right side is good. I then noticed that when I take the plug wire off the left side and just rest it on the tip of the plug (not press it on) it will fire fine on both cylinders, I decided to reset the timing (w/ boyer) and see if that is the problem. I then started it up and it fired on both cylinders. there was some popping an spitting so I adjusted the timing a small amount and then I had the exact same issue as before only now it is on the opposite side. (left side good, right side no fire) and same issue w/ plug wire. I undo the small change in the timing I made and still nothing. I have changed the plug, wire, and coil on the side that won't fire with the wire on the plug with no luck. Any idea what may be going on? Could it be a bad ground somewhere?

Click to expand...

1. It works on the RH side but not on the LH.
2. Fiddles with timing (via Boyer?) and then it works on the LH side but not on the RH.
Conclusion : It is the Boyer and associated wiring.
Ta.

blipJC said:

I changed the plugs again cleaned the kill switch still no change. was about to give up for the day and thought I would increase the gap on the plug (about double) and it started to fire. I went for a ride and had all the acceloration back. After about 20 min it started to sputter and loss of volts from the batterie and stalled. I got it home and checked w/ multi meter and was just over 10 volts. got it running and checked again and was down to 7 to 8 ish volts w/ no change when revving to 4500 RPM, turned it off and was back to 10 volts. I just put in a new batterie, rotor and alternator this year (new wire harness last year) because of the same issue w/ the batterie last year. Guess that wasn't the problem and I am back to tracking down some mystery electrical demons.

Click to expand...

Here he says the problem is a non charging battery....Low voltage problem with ignition..

So I tracked down the charging issue to a broken wire on the new alternator I just bought. I stripped the wires and soldered the broken wire, used heat shrink on the wires separately then again together. seems to be getting a charge now. With the bike at idle it reads about 12.6 ish volts and 13.8 ish volts with lights on at about 4500 RPM. Still a little popping around 2000 to 4500 RPM but it may be the timing and or plug/wire issue on the right side. at least I am now able to ride it again. Thanks again to all, I probably would have given up by now without you.

That popping may be a pilot jet adjustment issue...