I'm troubleshooting a scooter for my little brother. It's his main source of transportation right now.

It has a resistorized spark plug, which is not OEM spec - it's supposed to be a non-resistor plug, and 1 step hotter heat range.

Would the presence of a resistor be enough to cause weak spark? The secondary coil is rated 10K-15K Ohms at 68F and read about 20 at 45F. Seems like it's within range, and I am getting a weak, but present spark. Adding a 5K resistor into the system is going to cause it to jump 25% total resistance...

On the same issue, if we spray ether straight in the intake, or in the spark plug hole, would any spark set it off, or would it have to be a good one?

We've got it down to probably being either a horribly weak spark, or a short intake valve. It has compression, the carb is clean, but has choke issues.
When cranking the engine, I can feel a good amount of suction in pulses where I would expect to feel pressure from exhaust. Any tips? The guys at the scooter forum haven't replied to any posts.


My next steps are replace the plug with an OEM spec one, then get a shop to check valve lash. I'm out of town, or I'd forego the shop.

Thanks
William
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1990 740 Turbo, on its way to stock specs, maybe beyond