lpg woes

right... 3.5 v8 carb ran fine on gas and ran very lumpy on petrol then not at all, a week or so ago i noticed the truck overheating so i checked radm stat and water pump and all fine, sniff tested the coolant and no combustion gasses present. so yesterday i took the truck for a climb to stress the cooling system and it spluttered and would only run on tickover any more throttle and it bogs down and cuts out. so i stripped the carbs and they are fine and took off the dizzy cap and it seems to be in need of a new one....cleaned the points up and tried to start her up, nothing so i took a plug out and it was covered with brown carbon looking stuff and gave a weak spark, so off down to motor factors and bought ngk plugs, set gaps to 0.25 and fired her up, runs sweet as a nut on petrol,loads of power and sounds mint however the lpg still wont run on anything more than tickover.


so my questions are;

would dirty plugs cause my engine to overheat?

is the spark plug gap of 0.25 right for lpg and petrol?

and does lpg need a better spark to ignite?

thankee

sent u a photo of Autodata rec's by FB pm

cheers dude