Yup, those style baffles are pretty ineffective at quieting down an exhaust. They also tend to create a "poppy" kind of sound. Not my favorite style for a single cyl. engine. For engines that have a natural tendency to get this kind of sound I prefer a "chambered" style exhaust. It tends to create a smoother exhaust note. The packing that
should be around it also has a tendency to burn up and blow out, making it even louder. My Jardine had a very similar type of baffle (I'm the one that modded mine).
If there was a "doughnut cap" on the end that was cut off it's going to be difficult to quiet it down. You need that cap to seal off the end. You can take some measurements and go to the local auto parts store and try to find an exhaust reducer that will just fit inside your pipe (it needs to be snug) and can be welded to the baffle.
You may try punching a tab down into the center opening kinda like a "Screaming Eagle" Sportster baffle. This forces some of the exhaust gasses to go to the "outside" of the baffle and it then goes back into the center core (and out the end of the exhaust pipe) via the louvers that are punched into it.
Anytime you can divert the flow of the exhaust it will lose some of it's sound energy and become quieter. If you can maintain a smooth flow and not cause a lot of turbulance you can maintain your power as well.