hi ramos,glad you changed the oil!,i wouldnt bother checking the valves clearance yet
you say it fired up so you must be getting a spark and the timing must be near on
the mark all this you can check once its running i would connect up a clean supply
of petrol then try and start it and get it running its no good just putting petrol
in the lines it needs a continous supply rig something up or put the tank back on
then try it if no go then look for other faults