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Off Topic - PW50 Help

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My son's 1981 PW50 is driving me crazy. It has always been very unreliable, and now it just won't start. In the past a new spark plug with a tight gap would get it running again. Here's what I've done:

1. Cleaned carb - main, pilot, choke circuit, needle, seat, low speed air, etc.

2. Checked flywheel and keyway, looks good.

3. Replaced spark plug cap. Have tried resistive (5K) and non-resistive caps.

4. Replaced handlebar mounted stop/run/start switch.

5. Checked all wiring connections.

Here's the thing. If I hold the spark plug wire near the head (without a spark plug cap), I can see a spark when I kick it over. When I put on the cap and a BRAND NEW spark plug, with the plug firmly touching the cylinder head, no spark. If I hold the plug so that the center electrode is near one of the head fins, the spark will jump from the center electrode to the head, but will not jump the gap to the ground electrode on the plug.

I opened up the gap, filed both halves with a points file, and did the same experiment. This time the spark visibly jumped the spark plug gap, albeit weak. I put the plug in the bike and it ran for about a minute (poorly) then died, and it will not start again.

Inspecting the plug afterwards shows it to be wet and oily.

I am suspecting a shot coil or the winding under the flywheel. Does anybody have any suggestions? Does anybody have a shop manual for one of these that gives the resistances?

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the spark is too weak. I would say a shot coil or the wire is corroded, chewed through, etc. Possible that there is dirt and or corrosion between the magneto and the magnets too.

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Unplug the white plug on the Start Run Off switch and see what happens. Sometimes it gets wet or corroded and your bike wont run. Leave the single plug with the black wire plugged in so Off will kill it. You can start the bike and ride in either Start or Run.

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same thing happened to my bike.. It would run for almost 5 minutes before bogging out b/c the coil was bad and overheating. A new coil should be your fix

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