My grumpy Disco

Hi i bought a set of blue 10mm v8 leads at Billing for about £75 including spark plugs. when i switch to gas the power drops drastically..i found if i put the old king lead on it works fine..almost..ive checked the lead and its seems OK..could it be the coil just does'nt like the bigger lead...mmmmmm..anyway the help i need is..does anyone know the size of the gap on my plugs,,i,m told point 8th of a mm but i only have feeler gauges in thou...thanks..oili 123

plug gap is about .8mm i normally do it by eye, lpg will drop power as it burns differently to petrol, but if you fit your old king lead and it improves then maybe you have a high resistance in the new king lead, could be the coil but i doubt it, doesn't matter what leads you have, the coil should work as before