MOPED ARMY

Update: when I paddled, the engine makes low roaring sound... Light is on. But the moment I release the throttle, it’s dead :(

the short burst could be some backup or blowback. it can happen if for example the gas is leaking thru the carb and pooling inside or conversely if it's not got enough fuel (is gas on?) als happens if the spark's erratic and not at the right timing, I'm suspecting tho the new carb is maybe leaking and flooded it, i'd check spark and see if any liquid comes out the pipe or blows out when the plug's out. or maybe just no flow, so you can check the drain bolt under the carb while it's all still assembled.

I mean have you verified that the spark plug is actually firing as you pedal? See the "Basic troubleshooting" section of Fred's Guide. (edited)

Spark is good, just tested it. Unlike before, the engine makes low and loud noise. Paddle is harder to step now....

On the video it sounds pretty normal to me tbh. Up until ~15sec it sounds like the throttle is open, then it sounds like the throttle is closed (less "throaty")

Is your decomp, properly seated? Pull the sparkplug out and re attach it to the boot and rest it on your cylinder. When you kick the bike over it should make a spark visibly from the tip of the plug.

Check that before you go removing any flywheels to inspect the seals.

Also, you replaced the carb. Why? Was the original broken? What kind of carb did you replace it with? What jetting is in that carb?

Thanks for all the info! Will check into these possibilities...