Nah. That's where the choke plays a part.
The petrol is injected under pressure, obviously.. so warm or cold the particles are going to be roughly the same distance from eachother... UNLESS we're talking about a 40+ degrees hike, here.
Either way, cooler petrol would be slower moving on a molecular level and molecules would be closer together.. for the most part I think cooler fuel would provide a bigger bang per ignition. But as I said, I doub't temperatures are ever going to be extreme enough; one way or the other, for it to play a big part.
Edit: Logical thinking would imply that warmer fuel would react more erratically to sources of ignition.. but I'm just not sure that would be the case. Liquids of a certain density flow and change state easier/quicker when heated. Hmmm