Boat leak

I may have a boater's worse nightmare. I have a 2000 model Bass Tracker 16.6 ft. with riveted hull. This boat has been dry as the desert until recently. I needed to check a couple of things, like plugging my live well to make sure it is not leaking, but how would you go about finding a leak if in fact, I have a bad rivet somewhere?
There may be no connection whatsoever, but I will mention that this started about the time I upgraded to a larger outboard. The new motor is about 90 lbs. heavier than the first, but the boat is not overpowered.(Went from a 25 Merc to a 55 Yamaha, both 2 stroke)
I can't see where it sits low enough from the added weight to cause water to come in.
Any suggestions on troubleshooting?
Thanks,
SeaRay

Check all your water lines and fittings in your aerator system. The fittings can crack and its very hard you see at times. If all that looks good a common way to locate a leak is put the plug in and then put water in the boat until you can see where it is coming out.

Like Bill said, check the normal stuff like hoses but look real close at your livewell pump where it goes through the transom. When they were mounting motor they could have cracked the tube that goes through transom or the pump housing it's self. Also if you don't find something real obvious on the trailer, put it in the water on a calm day and check the bottom 2 motor mounting bolts to see if it could be leaking around them.

I agree with Barnacle Bill..............But if your model boat has foam floatation under the floor I would reserve the filling the boat with water for the last resort, You don't want the foam to soak up water if you can avoid the possibility.........

Couple other things to check, That may be unlikley but work checking out....... look very closely up front right were the bottom starts to turn up look next to the rivets and make sure you don't have any stress or fatigue cracks...... Also Did you swap the motors? if so check motor mounting bolts, If they are not as tight as when first installed that could be a sign of transom rot.........

If you just changed motors, be sure you got the speedometer hose connected. That can pump a quite a bit of water into the boat while running down the lake.

Well I took the morning to check things out. First, I plugged the outside hole that is the drain for the live well. I also plugged the live well on the inside. Two hours using the TM, no water. Ran down the lake a couple of miles at about 25MPH, no water. Took the outside plug out, no water. Took the inside live well plug out no water leak. Ran the outboard another mile or two, no water in boat.
This is somehow related to the bigger, heavier motor and having two people in the boat. It was just me today. I think when I have a passenger, the live well takes in enough water that when I am moving it overflows into the boat. Next time I have a passenger, I will plug the wells like today and run the same test.
Glad it is not a rivet or fracture somewhere in the hull.

I'm not familiar with your hull, But I wonder if when the boat is loaded with two people If you are getting a little splash over when you slow to a stop due to the bigger motor setting the stern deeper in the water............ or have you added anything to the transom that could be causing a spray over?