Langkjaer

My son and I, are in the process of repairing an older Yamaha SZR 660. Last season it ran fine, right up to a point where it would not start. It was set aside, but now we're looking at it, to fix the issue. We found that the bike, was fitted with an unoriginal electric fuel pump, and some wiring/relay for this. This pump was deemed faulty, as it could not produce pressure. We ordered a new fuel pump, which is an vacuum operated one, like the original one. To this also a set of new fuel lines, and a new fuel cock. After the fitment for these parts, a new spark plug, removal of wiring for the electric fuel pump, and some repairing of other damaged electrical wires. The bike will still not start. It cranks just fine, and if we spray some start spray, into the carburetors. We can then from time to time, get it to run very shortly. Where do we go from here? All help is appriciated.