I have a 90 indy 650 with pipes and studs and its clutched and my buddy he was useing his dads rev 600ho and we lined up and I beat him so I would think that if you have done anything to your mxz you prolly be able to take him. remember theres no shame in loseing either i lost to a 03 mxz700 three times in a row 
The 600HO will easily beat a reg 600. Also it wouldn't even be close between a 90 650 and a 600HO as the 600HO would walk on the 650. I am confused how your 650 could beat the 600 but lose to a MXZ700 as the 600HO is also faster than the 700
My dad bought a 2003 rev 600 H.O. and I just got a brand new left over 2002 MXZX 600 at the end of the winter this year. We went and dragged against each other and I beat him four times in a row. Niether of us were picked and he had 500 miles on his sled and I had 200 on mine. Just what happened with my experience.
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