Strange fuel issue

Someone accidentally put Diesel in one of our 3000 w generators , maybe about a third of the tank mixed with petrol , it now starts everytime with just one small jerk of the pull cord , much faster than before, though it runs OK with no smoke it's not producing full power , we are wondering how that Diesel in the mix causes much easier starting ?
 
It's not a problem as tomorrow the tank will be drained and fresh petrol put in.