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Old 07-10-2008, 07:46 PM   #1
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Default Help with Yamaha SR!


I recently bought a Yamaha SR125(93) from a friend who had it in a garage for about 4 years but had it out from time to time teaching his son to ride. A few weeks ago i began to notice it losing power (usually up in the higher gears) and dropping from about 65mph down to as low as 35mph and staying there! And more recently its been doing it more often, and even in 1st and 2nd gear (acceleration drops, big time!). Ive totally dismantled the carb and given it a good clean, checked and cleaned the air filter and drained the old oil and refilled it with new stuff, but i'm pretty new at this so i'm sure theres a tonne of other things i should be doing! So any help at all will be greatly appreciated! Because 35mph on a dual carriageway is very disconcerting...
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Old 07-10-2008, 08:36 PM   #2
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Sounds like it's losing compression when it gets hot. Probably needs a bore job and new piston/rings.
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Old 07-11-2008, 04:51 AM   #3
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Start with a compression check. That will give you a hint.
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Old 07-11-2008, 07:29 AM   #4
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Originally Posted by longride View Post
Start with a compression check. That will give you a hint.
But do it when it's hot. When the engine is cool, stuck rings can seal, but as the engine heats and the cylinder expands, the stuck rings lose their seal and compression and power go away.
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Old 07-11-2008, 07:31 AM   #5

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It's a two stroke, right? Check the timing, and for air leaks (base gasket, crank seals, reed block gasket, etc). If it runs good when it's cold, and gradually goes down the tubes power wise, that's an indicator of incorrect timing, or an air leak that gets worse (opens up) as the motor gets hotter.
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