weak/erratic spark By kingcricket (Read 5,283 times)

[kingcricket]

Have been working on my gf parents old scooter.  Not sure what year it is but it's a Schwinn collegiate 49cc, sat for a couple of months then wouldn't start.  wouldn't even putt on starter fluid and I figured the spark was too weak to fire I have it all ripped down all wiring is accessible.  So far I have pulled the wire out of the cdi that works the safety kill switches no difference.  Has a new pick up coil, stator, racing cdi box, and voltage regulator.  there is no battery hooked up at the moment testing it with the kickstarter and am even using a drill to turn the motor over.  I'm getting 58 acvolts from the stator for ignition, pick up getting .0acv  moved it as close as I can get it and now have .1 acv, 156 ohms resistance that's both from old and the new.  i don't know if I bought a bad pick up coil because I thought they were supposed to put out .5 acv, anyhow from the cdi to ignition coil I get 0 v but still weak spark at plug.  So I'm stumped any ideas I am new to the forum but I have always got all my help from reading problems everyone else has had, just seems like no one else has come across this problem.

I have also have run grounds to each other and checked for resistance all grounds get .02 ohms. 

[kingcricket]

the spark is weak it's not a big bright blue can't see it in the daytime but you can here it

[Bashan]

.05v AC should be enough though it's at the bottom of the scale, I'd like to see a little more voltage on that. 58 should be enough on the other wire. Did you try swapping a plug out? What do you mean you moved the pickup and it started working? How does one move the trigger? Rich

[kingcricket]

take one bolt out and move it closer and tighten just the one bolt just did it to check it to see if the volts would get better, because with just it being where it should I got nothing. funny thing is if I unplug the pick up from the cdi I have no spark so it must be doin something even though it reads nothing. then again I also have no volts at the ignition coil and still have weak spark so idk. there is no battery on it either I don't know if that would cause anything or not you'd think it would still kick start.

[kingcricket]

and my multimeter doesn't go down to .05 it only goes to ten thousands but I see post where it should get .5vac and other ones that say .05vac, not sure which one to go by, and yes I tried another plug and coil.

[Bashan]

You won't get absolute values working on Chinese scooters. Different manuals give different numbers. It does get frustrating. Go with .5v AC (see my below post, I changed this to +.05v AC!), if it's below that replace the trigger, they're cheap. I have no idea why moving the trigger would make spark, it shouldn't. Take some pictures of the bike, stator pigtail (need wire colors exposed), and the stator. I want to see if it's an oddball design. Can you give me the engine code also? Bottom left, front of engine. To see if the CDI is creating a spark, unhook the yellow/black from the coil. Put a probe of your multi in the end of the wire and ground the other probe. Make sure your killswitch is on run, turn on the key, crank it and see what AC voltage you get. It should be about 30% of what the red/black tested at. If you have a decent trigger value, above 50v AC on the red/black, good CDI grounds, and you're not getting squat at the yellow/black coil feed, it's 90% probability that the CDI is toast. Rich

[kingcricket]

moving the trigger didn't give it more spark I was just seeing if I would get more volts out of that brand new trigger. I have tested it with 4 different cdi boxes two of them brand new. its dark out now so i'll test the yellow/black wire in the morning, that's the wire I was testing and getting nothing from but I never unplugged it from the coil. I can get a picture off the bike and numbers

[kingcricket]

didn't get a chance to check the scooter brother called about a spark problem with my nephews off brand Chinese 4wheeler. funny thing I wasn't getting any reading from his trigger coil either so we put the 4wheeler up on its side to get to wires easier and I unplugged the cdi box to check power from stator was getting 48 volts plugged it back in no spark no volts leaving the cdi to ignition coil. brother plugged In a plug for back tail lights that was unplugged and was trying to trace wires to make see where the plugs all went and checked it again just to see and had beautiful spark. unplugged the plug that he plugged in thinking it was the problem and it still ran, but I checked volts while it was running and was getting .02v at the ignition coil 70v at the stator and .01 volts at the trigger coil, but still running perfect they did about 10 laps around the yard parked it and it still started back up. But judging by the readings it shouldn't even run.

[Bashan]

I was looking over some of my old notes and I ran some tests a couple of years ago, and indeed, I was getting spark with a .05v AC trigger, so ignore what I wrote, sorry, it happens. .05v AC trigger voltage should produce a spark if everything else is working properly. I would like to see more obviously but it should work. This is how you test the ignition coil. If your multi isn't upper tier it may not be able to read the pulses to the ignition coil, it's a bizarre waveform. If it's running, the coil is getting some juice. The brake light shouldn't affect the spark, you must have bumped something and got a connection to touch again, maybe a ground. Engine ground? Have you checked that, I'm just spit balling here. Rich

[kingcricket]

I agree and believe it is a ground but I've been all over the wires have checked and tested for ohms on all ground and making your if I touch bare spot in the frame I have .02 ohms on every green wire on the scooter. that's why I say its crazy I just can't find the problem.

[kingcricket]

thought maybe a handle bar switch might be bad I don't know if any of the headlights wires could ground out on the handlebar and enable bad spark. I don't know how I could by pass the lights for the power or if I could just disconnect the yellow wire from the stator that powers the lights I don't know if that would need to complete a circuit or not.

[kingcricket]

and I tested the yellow/black wire unplugged from coil and while the motor turned over I got 19 15 12 10 9 5 2 then it stayed at .02vac.

[Bashan]

I think it's your CDI man, that's a really erratic output on the yellow/black. And when it bottomed out at .02 that tells me the capacitors discharged what they had and then they recharge cranking it and the process starts again. I hate to have you just swap parts but there is no real test for the CDI, a multimeter can't get in there. Even in the manuals it will say swap one out and see what it does. They're not that much, probably $20.00. You're giving it what it needs: AC power, trigger pulse, ground. It's just not giving back.....selfish jerk. Hey, did you try pulling the B/W kill off the CDI and see how it does? That would take the killswitch out of the equation. If you do that test you'll have to put it back on to stop the engine, or just use a jumper to ground that CDI port to frame. Rich

[Bashan]

OK, I checked my wife's bike, a 150 Puma. I put one lead in the end of the yellow/black while it was unhooked from the coil. I then grounded the other probe on the frame. I turned on the key and cranked it. I got a rock solid 54v AC. It didn't fluctuate but maybe a tenth of a volt. I cranked for about 20 seconds and it did not start coming down at all on the volts. This is a normal test, yours was abnormal. I have a three phase stator on this bike so it's going to read a little strong. But if you had approximately 30 volts and it stayed there, I would be comfortable with that. I'm convinced it's your CDI. By the way, the .02v AC is what I call system background voltage. You will find that when testing some components there will be a slight voltage reading when the key is turned on. The Puma did the same thing, exactly .02v AC with the key on. That doesn't mean there is current flowing. Current is the actual movement of electrons and is measured in amps. Voltage is electrical potential, or the push on the electrons. You can push on them and have voltage, but if they're not moving there is no current. Is that right Dr. Rocco? Rich

[kingcricket]

See that's what everything points to but I had one cdi that was brand new and had bought another one just in case the new one was faulty, that would mean the two old ones were bad and the two news ones are bad. It's frustrating and really hard for me to believe that all the cdi boxes hAVE tested bad. I tested it again and it did that but down to 0v I switched the multimeter to dcv and went up to 9 and down to 0 then back to acv and 30 down to 0. I don't know everything points to the cdi, there not expensive but I already bought two and how many more would I have to buy before I get a good one. That's why I'm thinking something must be grounding out and throwing the cdi off. think they're should be a way where i can just bypass all my extra switches and just run just with the grounds and power from stator to cdi to coil cause those are the main wires to make it run. If i was able to do that and get good spark I would know it might be like my power wire from the lights grounding out and messing with the cdi. I've been messing with this for better than a month.