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Post by runnerboy885 on Dec 13, 2010 14:39:08 GMT -5
Hey Guys, First Post,
So I recently got a QM50Qt-B2 50cc 2 Stroke Scooter. When I first got it, I was told it merely need a carb cleaning and when the person I got it from tried to start it, it caught for a second then turn back off. I've been enjoying working on it for about a month now cleaning things, taking things apart, stuff like that, but I'm ready to start seeing results.
I put a new battery in the thing since the old one didn't hold a charge. Next, I took the carb off and cleaned it out, making sure I cleaned out the jets. Next, after putting it back on, I tried to fire it up. It would turn but wouldn't catch. So. I started trouble shooting.
Next thing, I took the spark plug out and cleaned it since it was obviously fouled. Next, I reattached it and tried to test for a spark. There was no spark across the gap. Damn. So next thing I tried was getting a new spark plug. Since it didn't spark even with the new one, I tried a new ignition coil. Still no luck...
Just for kicks and giggles, I decided to try and measure the voltage that reaches the ignition coil when I try to start it and it wasn't receiving anything really. Damn. So I decided well, there are only so many things I can replace haha so I also threw on a new regulator. But still no luck. Damn.
So here I am. I don't know where to go next and I was hoping for some help. I thought it might be the cdi but I can't find one on the scooter. So what are your opinions, guys?
P.S. Please no "LOL Chinese Scooter? You expect that to run?!"
I'm aware it isn't a good machine. Regardless, I'm going to make it work.
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Post by lshigham on Dec 13, 2010 14:41:38 GMT -5
I think it's either a short or the CDI.
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Post by sportsman matt on Dec 13, 2010 15:08:13 GMT -5
On mine the CDI is in the battery compartment, flipped upside down so it blends in with the battery compartment itself. Check there, the other place they like to put it is next to the tank along the frame.
I had the same symptoms when I installed the new engine, turned out there were 2 wires with bullet connectors on them, and the color codes don't match up to the OEM wiring. First attempt the wires were in the wrong position, no spark. Reversed the two and plenty of spark.
Just something else to check also.
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Post by buiditright on Dec 13, 2010 18:38:02 GMT -5
They also like to put them under the front cowl where the headlights are.. My UM is there. most all the others are as said either under the seat or in the battery dept .
Bill
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Post by runnerboy885 on Dec 14, 2010 13:15:40 GMT -5
Alright, I still can't find the cdi on the scooter....
Is there a wire I should be able to trace back to the CDI?
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Post by erictheviking666 on Dec 14, 2010 13:38:58 GMT -5
On mine the CDI is under the floorboard on the left side along the frame. You have to take of the side panels and lay on the ground to see it. To remove it I also had to take the plastic splash panel underneath off as well.
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Post by tortoise on Dec 14, 2010 14:20:01 GMT -5
Google . . might be looking for something the QM50QT-B2 does not have.
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Post by runnerboy885 on Dec 14, 2010 15:04:45 GMT -5
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Post by tortoise on Dec 14, 2010 16:40:33 GMT -5
Based on the above diagram link, test continuity of the white wire between the stator and ignition coil (49) . . looks like the key switch (7) is the only thing that grounds it out. Might also Ohm test the stator coil, but I don't know what the specification Ohms are. Edit: Testing The Stator Coil |
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Post by runnerboy885 on Dec 14, 2010 18:05:51 GMT -5
The wire between the stator and the ignition coil is continuous. Also, I tested the resistance on the stator coil and it was good around the correct resistance.
Any other suggestions?
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Post by tortoise on Dec 14, 2010 18:20:43 GMT -5
If you have not already done so, test continuity between cylinder head casting and battery negative . . to determine if spark plug is grounding properly.
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Post by tomcas on Dec 14, 2010 19:48:40 GMT -5
The voltage going to the coil comes directly from the CDI and stator. The voltage regulator has absolutely nothing to do with the ignition system. The first thing is to make sure all the kill switches are in the start position because the kill switch will not disable the cranking system on all scooters. If in doubt as to whether a kill switch or kill wire is bad you need only to disconnect the black/white wire from the CDI, which will enable the ignition system directly. If still no spark you can check the output of the stator and trigger coil by either measuring the resistance or by checking for voltage to ground while cranking. If the stator and CDI check out, and since you have already replaced the coil, then the CDI is the most likely suspect unless you have a bad ground somewhere. There are chart values to test the CDI but I've had mix results depending of the impedance of the ohmmeter used.
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Post by runnerboy885 on Dec 15, 2010 12:52:05 GMT -5
Yeah I just check if the cylinder head and the negative terminal are continuous and they are. By the way I really appreciate the help and I hope we can get this guy going. tomcasThanks for the help but most of what you were saying revolves around the CDI, which this scooter does not have. Should I try checking the voltage of the stator upon start up? If so how should I do that? Once again thanks for the help, I really hope we get this thing running. |
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Post by tortoise on Dec 16, 2010 13:08:02 GMT -5
Test continuity between the ignition coil mounting lug and battery negative to determine if the primary side is grounding properly. In theory, the magneto rotor passing over the stator assembly should induce stator coil voltage spikes for the ignition coil primary windings to induce stepped-up voltage in the secondary windings for plug sparking. If the pathway continuity is good, and the stator coil Ohm tested good but is NOT putting out voltage spikes to the ignition coil, that would indicate a grounding or continuity deficiency in the stator unit. |
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Post by tomcas on Dec 16, 2010 14:36:25 GMT -5
tomcasThanks for the help but most of what you were saying revolves around the CDI, which this scooter does not have. Should I try checking the voltage of the stator upon start up? If so how should I do that? Once again thanks for the help, I really hope we get this thing running. Oops my bad, I forgot it's an old chain drive. There's not much to it. Just the stator that's grounded at one end and a white wire leading to the ignition coil. As long as the white wire isn't grounded then it should run. For giggles just disconnect the white wire from the stator at the harness connector and disconnect the same from the ignition coil. Then run a jumper wire in it's place directly between the stator and ignition coil. As long as the stator and coil have a good ground you should be all set. You could even run a jumper ground between the two just to be sure. |
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Post by runnerboy885 on Dec 17, 2010 14:49:07 GMT -5
For kicks and giggles, I check to see what kind of voltage was making it to the ignition coil. I had checked this before but was checking dc. This time when I checked AC, the voltage went up to a nice ~20+ Volts. Now, the coil is getting the juice, but how much does it need? I switched from a single prong coil to a 2 prong coil and I think i'm hooking it up correctly, but I could be wrong. I really hope this isn't a UTS (User Too Stupid) error...
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Post by runnerboy885 on Dec 17, 2010 15:43:58 GMT -5
Alright, I also measured the AC voltage coming out of the stator directly, not across the wire to the ignition coil and it peaked around 24VAC.... So what do you guys think is going on?
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Post by tortoise on Dec 17, 2010 16:00:03 GMT -5
I switched from a single prong coil to a 2 prong coil and I think i'm hooking it up correctly, but I could be wrong. Post a link to an image of the coil, and describe how you hooked it up. |
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Post by runnerboy885 on Dec 17, 2010 16:17:06 GMT -5
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Post by tortoise on Dec 17, 2010 16:26:06 GMT -5
On the new one, I put the AC live wire on the small prong marked in green and the ground went to the prong marked in black. Reverse the wires . . green is ground on those coils. |
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Post by runnerboy885 on Dec 17, 2010 16:37:15 GMT -5
Reverse the wires . . green is ground on those coils. Thanks! Still no spark haha but that helps. |
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Post by tortoise on Dec 17, 2010 17:51:05 GMT -5
Have you Ohm tested the 2-prong ignition coil with probes at green coded prong and internal spark plug cap? Just want to verify that when checking for spark, that you are grounding the plug . . guidelines. |
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Post by runnerboy885 on Dec 17, 2010 18:29:53 GMT -5
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Post by tortoise on Dec 17, 2010 20:31:47 GMT -5
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Post by runnerboy885 on Dec 17, 2010 20:53:36 GMT -5
Alright, well what voltage is supposed to be coming out of the stator? right now the most I've seen come out of it is 24 VAC
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Post by tomcas on Dec 17, 2010 21:03:23 GMT -5
I think you're going to find that you can't just switch the type of coil. The reason is the coil you installed is designed for a CDI ignition which sends much higher voltage to the coil (like 300 volts). The original coil is designed for a much lower input voltage so it has a higher turn ratio. Simply put, you are generating too low a voltage to even bridge the spark gap a atmospheric pressure. Go buy the original coil www.partsforscooters.com/148-209 and next time you tell your story be sure to add the part about how you installed a new coil but that it was not the same style because it makes all the difference in the world. |
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Post by runnerboy885 on Dec 17, 2010 21:43:42 GMT -5
Sweet, if that works then thanks a lot!
Edit:
Before I order a new one, is there a way for me to check if the one I have is a dud? Like checking the resistance?
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Post by tomcas on Dec 18, 2010 9:01:45 GMT -5
Sweet, if that works then thanks a lot! Edit: Before I order a new one, is there a way for me to check if the one I have is a dud? Like checking the resistance? Yes you can check the primary and secondary coil resistance but my experience is that this is not 100% reliable. The high voltage can arc over internally but show up fine under a simple resistance test. So if you find an open (infinite resistance ) you can say it's bad but otherwise it's uncertain. Measure the primary winding resistance by going from the ground (metal part of the coil) to the input tab. Measure the secondary winding resistance by going from ground to either the spark plug connector cap or unscrew the spark plug connector cap and measure to the wire. Keep in mind that most spark plug connector caps have an internal resistor to supress electrical noise and typically these are around 4 to 7k ohms. Some times the springs that hold the resistor in place and rust away and create an open. If you find an open at the cap you can unscrew the brass screw inside and examine the resistor and spring. |
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Post by runnerboy885 on Dec 18, 2010 14:38:01 GMT -5
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Post by tomcas on Dec 18, 2010 22:40:13 GMT -5
The scale range you have selected to test the primary coil is too high. Drop down to the 200 ohm scale because the resistance could be a lot lower. |
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