The tank overflow just gets routed to keep fuel off of a hot engine, I just out mine right next to the engine .
I'm sure someone that has installed the unit you have can correct me if I'm wrong, but you need to connect the tachometer wire from the Acewell, directly to the ignition coil .
The GEN light needs to be connected to the light blue wire that is the wire from the voltage regulator, also the charging system will not work with an LED as the GEN indicator light, unless you have placed a resistor inline with the LED, the LED doesn't draw enough current to get the charging system going .
A fuel smell, may be over filled carb float bowls, or leakage at the various hose connections .
There also is a seal around the inside of the fuel cap, if it is the original, it may be hardened, cracked, missing, etc ....