Small gas engine with poor FMIC

[rotrex]

the stop and go issues come from the intake air correction of the ignition timing.
usually this is helped by fans running across the IC.
sounds like you should relocated the IC.
spraying at loads connected to city stop and go will cause issues with the water condensing everywhere as there is hardly any air flow. Direct port will not have that issue, but require you to map the ECU to take advantage of that, i.e. accept more timing at high intake air temperatures.
it also won't improve MPG at cruise speed unless you map it to run super lean with loads of ignition advance, e.g. an AFR of 20:1 plus water. Not worth the trouble.
Do you have full access to the ECU and can map it?
if you just substitute methanol for petrol, you save fuel, but use more methanol. With the cheap gas in the US, you won't save money.
Relocating the IC to see cold air will improve MPGs and help with the city driving.
I'd do this and add water meth under mid to high boost.