Honda Sl125 stops sparking at rpm

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[GS_in_CO]

Loss of spark under load (different from high RPM) can occur if the plug gap is too wide because a full charge of fuel/air mixture is more of an insulator than nearly-no fuel/air (=vacuum) so a weak spark or excessive gap can't make the jump at high power but it can at low power.

You might also have a gap in the conductor portion of the spark plug wire which you can't see which is contributing to an excessive gap problem.

I suppose that weak connections to the coil could give similar symptoms because at high RPM there is less time for the coil current to build up to create the voltage for spark so dirty connections or defective coil might give these symptoms too.

But check plug gap and plug wire first. They are cheapest and more likely than coil problem.

[Johnj]

The video says you need to look at the carb and or intake.

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[Johnj]

I'm sorry but you can't use silicone to seal the boot, buy new ones.
Did you replace the O ring between the carb and the engine?
There are many guide books on how to diagnose carb problems. The idle circuit is working but as soon as you twist in some gas (lift the slide) the engine dies (the needle isn't lifting off the seat) or bogs (the needle lifts too high) out. This could be as simple as moving the clip holding the needle up or down ONE notch.