Everything that has been explained to you is fine, but I prefer to go from the simplest to the complex, you would first have to measure the fuel pressure, in some systems you can easily regulate, with a screwdriver.
From what you say in your area there are no people understood or with adequate elements to address this type of cars.
But you can measure the pressure with any pressure gauge if you get an idea interspersed a "tee" in the naphtha circuit, (make sure it is the entrance and not the return.) I do not remember the exact pressure but it is about 1.5 kg/cm2, in any case if the pressure exceeds this limit can happen that the gasoline engine is flooded.
The regulator is next to the injector is generally a lid with 4 screws in which they are adjustable have a screw with a scoop for screwdriver and unscrewing down the pressure.
If it is not of this type, disarm it carefully, it is very simple, it only has a spring a diaphragm and a valve, clean everything well, it controls that the return output is not clogged, as well as the line that returns to the tank, if there is nor there is no clont obstruction, it starts and controls the pressure again, if it remains high, the regulator changes.
If the pressure is within normal values you will have to control the Lambda probe, but for that you will have to get a qualified technician.