There is a mixture adjustment screw between the fuel distributor and metering flap which is a 3mm Allen key i believe. You can turn it clockwise to enrichen, anticlockwise to make it lean. Only problem is there is no real way of knowing exactly what the mixture is set to, so your best bet is to take it to a garage to be sorted out. I assume that there is fuel getting to the injectors when you try to start it?