Help please after building my zvh i keep killing number 2 plug after ticking over for about 5 mins from cold

Ihad no issues with killing plugs before rebuild and i dont know whether this is related but number 2 injector pipe was leaking from the union on number 2 injector where it bolts to the metering head so i cut the pipe and sweated back on the connection using a heat gun and i thought everything was sorted

I change the plug and everything is fine then after about 5 mins the car starts missing and i pull the plug out and it is soaked with unburnt fuel as the plug has stopped sparking

Ive changed the leads and its getting sill changing plugs all the time to try and sort this, when the car runs till the plug goes down it is fine with no smoke lumpiness or nothing.

Any advice much appreciated