daihatsu hijet 993 efi engine refit not starting


The engine fitted was not identical the exhaust on the new was only bolted in two places so i had to refit the old manifold. the distributor assembly was very different to my original and had only one pipe(vacpipe?0for the advance retard so had to refit old distribtor assembly to the new engine. Petrol goes cylinders have sparks to all plugs but it will not start.Where have I gone wrong? Is there any one who can explain the ignition timing to me
Please lease help.Martin