RE: Ways to increase the fuel volume to 125ml
increase the fuel line length and add a inline reservoir from a caster or Mugen.
benefits of longer fuel line is more consistent fuel pressure and tune as well allows the buggy to run better when on its lid.
Fuel line length is shortened when you add a reservoir.
If your bugy is more a basher and has a odd size tank it may be a good idea to buy a tank that fits from another brand.