Bill is quite right, increasing preload is a bodge which doesn't cure the problem, you need to stick the bike on it's main stand or a workshop stand and remove the fork top caps so you can easily move the forks through their full range of travel (and at all steering angles), if the mudguard or wheel contacts the exhaust at any point then you need to find a way to move the exhaust from the wheel/guard or vice-versa. If you can't then there are two issues, one, the bike is illegal and potentially dangerous, two, as Bill says, the exhaust is not fit for purpose and predator need to rectify or replace or refund (assuming you bought from them, it's correctly fitted and it's meant for that model, no offence or slight intended!).
Sorry it's not good news.