Well, I don't know if I would do it with a Jett muffler... you will lose your top end more than likely. A good way to experiment would utilize a tube that you could constrict, like a rubber muffler extension. Now that I know you have a Jett muffler, maybe you should try a perry pump or a regulator instead as others have suggested, since the whole back pressure deal is purely a fuel delivery thing. You really should try the onboard glow. Just a quick & dirty setup you can remove easily... maybe that and a little leaning of the low end.