alto fuel pump is very robust and there is no filter in it.....thanks to PS.....anyhow if plugs have been checked then check distributor cap for cracks or scratches ....if present replace it.....also check distributor rotor that its advancing smoothly and is neither too sloppy nor stuck .........then ask electrician to check each and every grip of wiring....may be thats loose or sparking.....u can also check advancer wiring and advancer if its ff cng........or ask electrician to bypass cng system then check.