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75 Yamaha GPX 433 Meltdown

842 Views 2 Replies 3 Participants Last post by  Sled_Dog
A friend of mine has a 75 Yamaha GPX 433 the he recently rebuilt the top end and carbs...after about 3 hrs of riding it burned a hole in the left piston...some say it is a crankcase leak, another (very knowledgable man) says definitely the carbs weren't balanced.....any experience with this? any thoughts?
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Sounds like detonation damage, could be caused by too lean of a condition, wrong jets, timing too advanced or bad gas (too low of octane).

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Edited by - rtkatzl8 on 13 Jan 2002 15:17:31
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prolly running too lean. I don't quite get the unbalanced carbs. I mean they could have been on different jettings and the one that burned up was way too lean.
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