Everyone, good day to you. I'm fairly new to using a scope and attempted to perform a secondary ignition waveform capture on my semi-old 4 stroke scooter.

It has a slightly bit of a problem. Engine stalling at idling and after releasing the throttle and coming to a stop. Backfires loudly after releasing the throttle at semi-wide-open on short distances.

I want to fix this problem by way of the scope - analyzing the waveform and understanding it. With your help of course, from the analyzing part.

Your aid will be greatly appreciated.

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Did the problem exist before the modifications? . Does it backfire thru the carb, or out the exhaust (after fire). From my limited experience I don't see anything wrong with you capture.

The problem did not exist before. The modification was done right after I got the motorcycle. As for the backfire, it was through the exhaust. I tried to reinstall the old oem plug wire and seems to work fine now.

Though I noticed that at some parts of the waveform, the firing line reached more than 30kV and the burn time was less than 1ms. From what I read on documents online regarding secondary ignition waveforms, "the height of the firing line should be between 5-15kV" while "the spark duration (burn time) should be between 0.8 to 2.2 milliseconds (usually between 1 to 2ms)". I'll try to make the mixture a little bit rich, replace the spark plug, get a new plug wire and report back.

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My guess would be that you have a carb jetting problem. In my limited experience you can throw all that out when it comes to CDI secondary waveforms. It's a completely different animal.

Thank you very much. It really was a carb problem after all. Everything works fine now.

LECHUM,  see it is fixed but back fires are usually lean burn (carb) or timing.

Then dropping down to idle from speed, pops is usually low fuel or plugged idle or secondary jet (forget the name off the top)

Also most likely the bike stumbles or surges coming up to speed until it hits the main jet, also.

Thank you for the additional info. I'll see to it that those are also checked. The motorcycle is now in the process of being upgraded again. Updating stock parts for additional performance also the old aftermarket ones. Better performance = happy rider!

lE-CHUM, THE JET I forgot the name of is the Pilot jet. And many times if the problem persists even with stock jetting you have to go to a bigger one or bore out the one you have.

Goes from Idle, to pilot, then main and should be a smooth transition. If pilot is (to small or plugged)  will back fire coming down instantly from full throttle as shutting off main jet if pilot is compromised the lean condition causes a back fire, then goes into idle jet, and if the shut down is too erratic might stall, but not usually.

The back fire is caused from the burn time being (so long) from a lean condition that firing event is still happening when Intake valve opens or in case of 2 stroke into intake.   The other case of course is if timing is off, but back fire for me at least usually involves one of the two.

The other down side of plugged pilot jets is running high RPM say down a Mountainn and turning off throttle you spend a lot of time in a serious lean condition which causes an over heat as engine RPM is still high, so yes need it fixed.

Have fun.