Chris Hogg wrote:

Our workshop
technician did that to his car during the petrol rationing of 1973,
and ran his car on propane. SU carb, IIRC; he just bored out the jet
and machined a fatter needle, although I doubt that modern carbs are
that simple to DIY modify, but modified carbs would be available
commercially.

DIY'ed hydrogen storage in a car would be quite a worry