Lost top mph and rpms

I got a 2000 700 xc was running at 8000 rpm and 90+ mph no problem going across a open area it had 10-58 weights and then I bought a Epi performance clutch for it came with a yellow primary spring and 10-62 weights, orange secondary spring and a Epi helix put that in and ran 7100 rpm and only 70 mph then after a few miles it started to bog on WOT figured out it was getting way too much oil fixed that and it still did the bog so I put it all back to stock and still does bogs probably need new spark plugs now but any ideas why switching the springs and weights would change it that much? The guy said it should still run at 8000 rpms would I have to rejet it then? Don't know need ideas

Lost top mph and rpms