Wow????? Please don't get uptight with the responses you've received when clearly you haven't asked correctly ... Thumper_Bloke also didn't know what you were trying to achieve and asked / observed with his post; "Is this a power-to-weight issue or a weight-to-handling problem? I think he's looking to lighten the bike to make it handle better?" Now that we all know the real requirement maybe you'll get the advice you require? such as; Replace the battery with a Zinc-Air unit, or use the YZ electrics Remove Starter Motor and lights. Replace exhaust system in it's entirety with a Titanium header / Aluminum Silencer Lighten your flywheel, (although this will have an effect on low speed driveability) There are a few more options depending on whether your requirement includes handling as against simply lightening the overall bike ie: sprung vs. unsprung weight, and will include your wheels, tyres, (including tubes), disks, swing arm, brake calipers and shocks.