Alpha Sports 50cc ATV No Spark - ATVConnection.com ATV Enthusiast Community



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Old 05-04-2018, 05:27 PM
Weekend Warrior
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Default Alpha Sports 50cc ATV No Spark

Hi everyone-

First post here, been lurking a while! I have a 50cc Alpha Sports Mini Cobra/Kolt I bought for my kids. They've ridden it for a few years and when I went to fire it up this year for a tune up, no spark! It's probably a 2000ish model, I don't really know.

So far I've unplugged the black wire to the CDI with no improvement. The tether safety switch in the rear is overridden, and the original key was lost so the previous owner simply wired in an on/off switch in it's place. I've gotten a spark once or twice, but oddly enough it's been when the handle bar kill switch was off, just from me messing around with it.

I took meter readings at the coil and CDI and here are the results. My meter does some weird auto ranging, so I just typed what it said rather than trying to convert and making an error.

Stator:
White/Red to black : .487 K Ohm
Black/Red to black: .850 K Ohm
Yellow/Red to black: .5 Ohm
White to black: .6 Ohm
Ground: 0 Ohm

Coil:
Primary: .8 Ohm
Sec at Cap: 3.5 M Ohm

The CDI on this quad has 7 wires, they are 3 bullets with black/white, black/red, white/red. It also has two plugs one with orange and black, and one with black/blue and brown.

I'm pretty stumped here, nothing I've done improves the no spark condition. I believe this quad is the same as the Polaris Scrambler 50, and going off the wiring diagram for that, I believe the stator and coil are bad. According to that the values should be:

Stator:
White/Red to black : 110 Ohm
Black/Red to black: 780 Ohm
Yellow/Red to black: .5 Ohm
White to black: .6 Ohm
Ground: 0 Ohm

Can anyone help? Wondering if I need to replace both those items. I haven't tested the CDI, not really sure how to.

Thanks so much in advance!
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Old 05-05-2018, 07:45 AM
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Location: Lancaster England
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Could be an earth to run CDI. Some bikes are, so you need to try earthing the kill wire to see if that makes it spark. I've never found ohming out stators to do much good. Open circuit when you should get a resistance, something is wrong, closed circuit when it should be open, again something is wrong, but widely different resistances to what the book says, doesn't mean much.
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Old 05-05-2018, 12:00 PM
Weekend Warrior
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I tried grounding the black/white wire while cranking, didnít change anything.
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Old 05-06-2018, 01:53 AM
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OK, I assume you have fitted a new plug? Try checking if the stator's exciter coil is producing AC voltage when the engine is spun on the starter. Try checking if the trigger coil is producing an AC pulse. If they are, check if the ignition coil is getting a pulse from the CDI, this should be quite a high voltage. If it is, change the coil.
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Old 05-06-2018, 07:02 PM
Weekend Warrior
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Yep tried a new plug. Also tried with the cap removed just using the bare coil wire.

Iíll try testing those next. Thanks for the ideas, ignition problems are not my expertise by a long shot.
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Old 05-08-2018, 04:17 PM
Weekend Warrior
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Ok tested the coil and stator output today and found 83 v on exciter coil, consistent 230 mV on trigger coil, no apparent pulse, 1 v on ignition coil. All taken while cranking with the starter.

Not sure what to make of these numbers, but it at least looks like the voltage to the coil is very low.

Please let me know what you think. Thanks a million!!!
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Old 05-09-2018, 03:33 AM
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The trigger coil just pulses a voltage as the lump of metal sticking out of the flywheel flies past, not all that easy to test, as your meter may be "averaging" but it should be more than millivolts, though they vary so widely in output, it is difficult to say what is good. I would guess either trigger coil or CDI is at fault.
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Old 05-09-2018, 08:08 AM
Weekend Warrior
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Ok Iíll just take the shotgun approach and replace the stator, coil, and cdi. That said, anything wrong with the eBay versions? The actual Alpha Sports parts are quite expensive, more than I paid for the quad actually!

Thanks again for your help.
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Old 05-15-2018, 02:58 AM
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The wiring colours are different, but if you can work out which is which, it looks like being the one for those circa 2000, scooter based two strokes. A pity, as all you need is the trigger coil with the blue wire, the exciter on your machine is working fine. I note the trigger is adjustable for air gap, are you sure your existing trigger has the right gap between flywheel pip and trigger coil?
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