My car sometimes doesnt start when its hot.

I was told the battery wasnt good enough so i changed that to a heavy duty one, the engine turns over ok all the time so its not the starter. its as if no fuel is getting through or no spark, but when i leave it for a bit it nearly fires, but doesnt, then i leave it longer and it VERY nearly starts but doesnt, then i leave it even longer (cooler engine) and it fires up. no real rhyme or reason.

could it be fuel vaporisation? if so, how is this cured? bad timing? how is that cured.

i need to get this sorted as its annoying and mildly inconvenient to say the least

cheers all

peter