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Discussion Starter #1
I was brought an Arctic Cat 300 engine from a guy at work. He bought 2 identical quads, neither running (but did recently said the sellers).

I rebuilt the top end piston, rings, hone, valve seals, and cam. Everything torqued per manual, timing set and valve lash set, cleaned the carb. I brought him the motor and we installed it together. The battery was dead so we used a charger with start function to try and start it. The motor would just crank and crank. Finally I pulled the spark plug, it was we with gas, cranked some more. It only will spark the first revolution, then will not spark again. I swapped, CDI, voltage regulator, and coil with the other quad. No difference.

I then found that if I remove the charger and pull start the engine, it will spark constantly. Even fired right up and idled smoothly, but it will not rev. As soon as I give it any sort of throttle it cuts out and misses. I went through the carb again, everything is clean and functioning correctly. I switched the CDI, voltage regulator, and coil back to the original ones, no change. Idles all day, but the second you give it any throttle it cuts out and misses.

Trying to diagnose and mechanical issue vs. electrical, while the engine was running, I hooked the battery charger back up and turned it on 5a charge. As soon as I did that, the engine died. Back to the no spark issue.

When I had the engine apart, I took the left side cover off to clean out the milky oil (engine had gotten water in it at some point and never had the oil changed), the stator and magneto appeared to be in good shape. No magnets loose or missing from the magneto and no scratches or issues with the stator.

I am at a point where the only thing I know to do is throw parts at it starting with a new stator.

If anybody has ran into this before and direction would be much appreciated.

Thank you
 

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I think I would go with a new battery first. He’s going to need one anyway. If it runs good with the new battery and then gets worse you’ll know the stator is bad and it’s draining the battery when it runs.
 

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I think sometimes the stator is working so hard trying to charge a bad battery there is no power left to run the engine
 

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Discussion Starter #4
I will try that first. But what has me dumbfounded, is why does it suddenly lose spark when you turn the battery charger on? This is not only when it is running.

If I am holding the start button with the charger on 50A start, it will spark once, the first revolution. That is it, no other spark the whole time you are holding the start button.
 

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I’m no electrical expert but it sounds like it might have some kind of regulator that once it starts running it only gets power from the stator or something. That is kind or strange though.
 

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Discussion Starter #6
I’m no electrical expert but it sounds like it might have some kind of regulator that once it starts running it only gets power from the stator or something. That is kind or strange though.
Tried the battery first, no change other than you could start it with the electric start.

Installed the new stator yesterday. Runs like a new machine now.
 

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Good deal. Now I know the symptoms if one of mine has a stator problem. Thanks for reporting the fix. It’ll help somebody else.
 
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