Time for carburettor check and ignition check. First off, spark plug.
Brown and dry, good. Here's a link to spark plug visual inspection.
0.4mm spark gap, probably OK.
Opening the carb housing revealed a pretty clean SI 24/24 carb.
I pretty much suspect that the carb setup is 100% original. I found the spec for original jetting on Scooterlounge, and also pictures of the SI24/24 on SIP Scootershop.
Air jet 160. Standard. (Below this the venturi and main jet sits, did not take these out).
Idle jet (slow running jet) says 50. Standard.
The only suspect thing I could find was a hardened rubber petrol hose. The hose was jammed between the chassis and the cylinder cowling, making it impossible to take off the cowling. The petrol hose will be replaced when the new tank is in place.
As far as leakage goes, the carb housing, on the back side, there is a hole with a rubber plug. Beneath the rubber plug is a screw for adjusting mixture. Seems the leakage causing at least part of the motor sweating comes from here, perhaps from a flooded carb. This brings us back to the home made new crane installed on the tank, which again possibly means that the floater device / floater needle is defect. Very common problem. I'll keep an eye open. I might just need to clean and open the carb.
As far as ignition and cables, I've just done a visual inspection of the connectors.
Cabling seems original, and untampered with luckily. I was a bit suspicious with the connection box mounted on the engine, as it seems like cables should pass out on both sides.
Turns out the cables go down into stator instead.
OK, no surprises. But still no cure for the full throttle issue. Next on list to check: Cylinder and exhaust.