Hi guys, long time stalker but first posting. I'm making this out desperation. I've got a 1980 CM400 with pod filters. Recently replaced the exhaust with a Mac 2-1 and replaced the head gasket with an Athena brand gasket because it was leaking oil externally. Afterwards, it started backfiring through the carbs so bad that it would push them out of the intake boots. Triple checked the timing and it seems to be correct, so I figured it was the carb jetting because of the new exhaust. I ordered a jet kit from 6Sigma that is supposed to be made for this setup (127.5 and 80 jets with needle shims). This seemed to make it run worse. It idles fine if the choke is halfway out, no more no less, and dies if given throttle. I just did a compression test and found that both cylinders are only making about 80 psi, but the cylinder leakdown test only shows about a 10% loss out of each cylinder with no leakage through the valves. If anyone has any ideas what the problem might be, please let me know.