Recently it's been taking a long-ish time (3 or 4 seconds) of cranking for the engine to fire when it's cold.

We have Elko injected LPG but the car starts on petrol, so I don't think it's that. The oil, oil filter, front plugs, air filter and fuel filter are 2 weeks old, the dizzy is only about 6 months old and the battery 18 months so I don't think it's any of them!

Any ideas? It starts in a second or so when warm.