Strange issues with my old Falcon 72, a combat flying wing with a OS 25 FX.

I built the Falcon per vendor instructions, including putting in a bit of up thrust on my OS 25 FX, just a few small washers under the front mounting screws so the motor is pointed up slightly. Anyway, it flew well, but was a bit nose heavy. Thus, I added some weight in the tail, 7Gx6.

I did notice that before the model built up speed it pitched up, but at speed is was level with a slight bit of up trim for flare. At full throttle, it flew great, perfect for a combat plane.

In order to get some more speed out of it, I put a Mousse can muffler on it, and took it out for a test flight. Indeed it was faster, but two new behaviors show up. First, the plane seems to want to dive to the ground at full throttle, and is not as responsive to up input. It’s no big deal, just throttle back, but not good when in a combat situation. Second, it seems to want to roll left now, which I corrected with trim, but it’s strange that it was pretty even before.

Question, do I need more up engine thrust? Can idea what is causing the model to roll left? I checked the alignment, it dead on right down the center.

I'm going to remove the Mousse can muffler, and check it again. I guess I can work from there.

Thanks.

Did you check the CG after adding the new muffler? It's sounding like it might be nose heavy. Not sure about the rolling though.
Dennis-

That is the first thing I checked. It's fine.