It's actually closer to 9% (8.9%), which is what you get when you divide the four outs by the 45 unseen cards.
I suspect you were using a "random" card in the fourth spot for the first player, i.e.:
In this scenario, the first player essentially gets two draws (one when the hand is filled out with a random card at the beginning of each iteration, and one in the draw). Thereby almost doubling his outs, and, therefore, his equity.
For this type of calculation, you should fill out the hand before starting the simulation, i.e.:
Mark
Last edited by mark100net; 09-17-2017 at 07:23 PM.