OzVMX Forum
Clubroom => Tech Talk => Topic started by: cambo on January 23, 2014, 11:17:07 pm
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Hi guys,recently bought a 73' yamaha mx250 ,at first it started easily but the other day i found it hard to start.Kicking back badly at end of stroke it finally fired up and as i let out the clutch it took off backwards then stalled.I kicked it straight away and it then run correct direction,it then run out of fuel and i could not restart after refuel. Checked spark ,is a bit weak i also noticed cdi unit is leaking resin over swingarm,i have a spare one came with bike but it too has lost its resin .Has anyone experienced either of these 2 problems? and i did check stator plate seems all tight in there,any help appreciated.
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You are answering your own questions with the cooked CDI units,
Left field it could be sheared woodruff key allowing the flywheel to have moved with a resulting misfire
I doubt the magnets in the flywheel have moved but anything is possible
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I had a couple of Bulties that would run backwards not very well but enough to give you a bit of a frieght. i bump started the old metralla rolling up to the lights after stalling it on Burrwood hwy near the tech school stopped stopped for the red gave it some gas on green and went wtf as it took off backward the only thing i could find was a bit much advance on the timeing.
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I nearly rode my Sherpa into the neighbors pool backwards one day, was common with Sherpa / alpina with all the flywheel, as if it didn't quite make it over tdc, the flywheels would give it enough inertia to push over backwards, the ign would fire it and away it would go. rough running due to the timing but run they would. good party trick if you could get it right..
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ok son,thanks i will check woodruff key on rotor,but was this issue of the cdi common with old bikes or has it been fried ,overvoltage to cause resin to melt?
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Cooked the CDI ( Black melted resin over the swingarm ) on my YZ250C a few years ago. Don't know what caused it. Bought a NOS one and no problems since.
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The early trail 250/360 cc Yamaha's fired at only 2 degrees BTDC so poor tune or wear and tear made a few play the reverse running trick on very surprised riders :o
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My Bully Metralla flicked over backwards, years ago, long,slow idling at city traffic lights, got a bloody shock when i went to take off !!
Foss
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Old MDMCC story from'standing start quarter' days at the Castlreagh airstrip. A bloke at the start line on an old Bantam 125, one million revs, fed the clutch into it and went straight over the handlebars.
cheers.
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I bought a YZ125L that ran backwards. Strong spark. Fiddled with the timing for ages - either it would run backwards, or not at all.
Then I noticed that the little direction arrow on the flywheel was pointing the wrong way. The FW was from a YZ125F...
Put the correct flywheel on it, and problem solved.
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CDI on the way out probably due to intermittent problems withone or both coiloon the stator. Same thing happened with my MX360A replaced the CDI but kept having intermittent probs with electrics, finally found a drop in 25% power on the low voltage coil.