Diminishing output from CDI - 30 Volts to 2 Volts
 

Hi
I'm having an odd problem with my 50cc GY6 that maybe someone here can help find the solution to.
It's a no-spark situation, and here's what's going on - The stator is working normally, putting out it's 80 volts. The CDI is receiving the 80, but starts by sending 30 volts to the ignition coil, and that quickly drops to 2 volts over the course of a few seconds.
The CDI is new and another new CDI was tried with identical results.
The ignition coil is also new.
The CDI has good ground, an additional ground wire has been spliced in just to be sure.
Everything else on the bike is working normally. Lights, turns signals, horn, etc.
The trigger coil is also new and working.

I'd really like to get this bike back on the road ASAP, so any help is appreciated.

check the reg/rectifier

All done in less than 3 pages and countless voltmeter readings

That's new also... The connector is a good shape and seated.

The power wire for the CDI does not pass through your regulator/rectifier. The R/R has nothing to with spark. Gradual loss of spark usually points to the pickup coil just above your flywheel. Should be a blue or blue/white wire from your stator. Voltage should be about .5v to 1.0v. An anomaly with the pickup coil is that after a few firings or when they get warm from running...they lose voltage because the coil is faulty or stator voltage to them is irregular or too low.. This means your CDI may not be firing at the proper time i.e. late, at which time some of the current in CDI's capacitor has bled off giving you a weak spark. So get out your multimeter and check the pickup coil voltage.
Glenn

The pickup coil is new also, and has checked out ok. However, since your description fits the problem I'm having I'd say it was worth another look. Would a few seconds from a cold start (attempt at starting actually...) be enough time for the trigger coil to warm and fail? I haven't kept the starter running for more than 5-6 seconds at a time, and the drop occurs immediately. Also, if I try to start it again immediately afterwards, the power from the CDI doesn't start out at 30Vac, it starts either at 2Vac or slightly above. After sitting for a while (I've never noted how long it takes) then it will return to starting at 30Vac then dropping. That seems to fit in with what your saying if it can happen in that span of time.

Remember.. a pickup coil is just that..a coil..so anytime current passes through it the resistance from the windings creates a secondary condition besides a magnetic field..that being heat. Heat as you know is an enemy to any type of coil as it reduces its output. Hence the reason Electrical Power Sub Stations have oil cooling or liquid cooling for their transformer coils.
New parts or not..many arrive unserviceable.. I order CDI's for example in lots of 10 from my wholesaler..and always 2-3 of those are dead on arrival. Chinese QC is not like Japanese..German or Italian QC.
Lastly by trade I am not a certified mechanic..but a retired military medic..who later became a cardiac nurse..then gave that up to run a scooter parts/repair shop. It's just me so I get to be my own boss and everybody enjoys working for somebody they really like..lol..:D But..anyway..the above is my 2 cents. I see pickup coils fail often and they exhibit exactly what you describe. Lets hope it is a simple as that. Btw..what was the voltage you got from your pickup coil initially..then again after the spark weakened after a few cranks on the engine. If you see a voltage difference before and after that..well you pretty much have all the evidence ya need I would think..:hmm:
Glenn
P.S. Does the hot wire from the stator to your CDI also drop in voltage after a few cranks? Cause the stator is a coil too..so all the above things that affect a coil..will affect that coil as well..

So you promoted yourself right on to President and Janitor! :) I like working for myself, but my boss is a demanding tyrant...
The stator seems fine, it's showing +/- 80Vac consistently measured from the red/black wire at the CDI connector.
I'll have to measure the trigger tomorrow, I hadn't thought to check it in comparison to the CDI output. I don't know how useful my VM is going to be at measuring that small and brief of a voltage, but we'll see what happens.
One other thing - What are the odds of the trigger problem being in the magneto rather than the coil itself? I've tapped it with a small screw and felt no pull from it at all..

If your volt meter is digital it will capture the tiny burst of voltage..analog meters can't..nor do they work for the spark impulse from your CDI as it all happens so quickly.. Anyway yes..when you notice your CDI voltage drop..IMMEDIATELY check the stator output voltage for the CDI.. Chances are it has dropped as well..hence the reason your CDI output decreases. Let us know what you find..

Checked the trigger and it's showing a steady .1 vac with 185 Ohms. The stator is steady at right around 80 vac.

Here is a link to something I had them put in the Tech section on another site. There is a typo in it. I meant to put .5v for the pickup coil..but it shows .05 instead. But anyway maybe it will help? Here is the link to the Tech article..
http://49ccscoot.proboards.com/threa...park-condtions
:tup:

While looking into this, I've seen .05Vac about as often as I've seen .5Vac as the minimum useful output from the trigger coil. Knowing now that it's .5, I'd say the trigger coil is bad.
I've ordered another and will post again once it arrives and I get it installed.
Meanwhile, a musical interlude...
http://www.youtube.com/embed/5MtdIO23MKM

Kick @ss..been looking for that Video on you tube..:tup:

Any luck with your spark issue yet?:hmm:
Glenn

The new trigger coil arrived Friday and I installed it that evening. At first it did produce a spark and would run a bit with some starting fluid, but then I decided that since it had been sitting a while and I had a carb rebuild kit handy, I'd go ahead and use it. So after cleaning it and installing the new part, I put the carb back on and tried nudging it back to life with another shot of starting fluid.
Now it isn't sparking again. What's odd is that the sator is now showing around 60Vac instead of 80. Only about .1/.2Vac is arriving at the ignition coil.
I took the stator and magneto from another bike, put them on the bike I'm trying to fix and got the same results from the VM. This was with the trigger coil that was on the donor bike.
So right now I'm out of ideas. The new trigger coil did produce a spark, the bike tried to start then suddenly, all on it's own, it's back to not sparking.

.1/.2Vac is arriving at the ignition coil?? Well we know that is not good and won't arc. Stator is down from 80V to 60v..:hmm:.odd. But it started to spark then stopped. Tells me something is shorted and burning a wind in the pickup or stator...possibly. Even a stator with only 60 volts will excite the coil and induce a spark. Weak yes..orange in color but it will be there. The only thing between your stator and Coil is the CDI. But you said you swapped CDI's so that rules out that the Electrolytic Capacitor in the CDI is bad. This sounds to me like a bad ground..or a short to ground from a hot wire. Usually the short to ground is found in the kill switch wire in the handlebar switch set or CDI itself (from my experience) Sad to say but my Dad was an Electronics Engineer and you got stuck with me.. The one who chose the Medical field vice the Mechanical or Electrical field. He did drill me hard as a kid on Watts..Amps..Volts..Current..Resistance..Ohms law and all that stuff. But still..we WILL figure this one out..:tup:
Glenn