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Old 05-18-2009, 10:27 AM   #1
Sir Not Appearing OP
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Question What are symptoms of valves that are out of adjustment?

My girlfriends '83 Yamaha XS400K Maxim has become increasingly harder to start and when it does start, it dies randomly while idling. The carbs were professionally rebuilt and when it will actually start, it runs great from idle to redline but you can't let it idle for long or it will die and then good luck getting it restarted.

I'm thinking its time to check the valves. Are these symptoms of valves that are too tight or out of adjustment?
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Old 05-18-2009, 10:38 AM   #2
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Certainly doesn't hurt to check.

Valves out of adjustment can make bikes act up in many ways, and will often increase the effect of other issues with carb tuning, ignition performance etc.

You may be able to check it with a compression tester, as too tight will leave valves slightly open.

But for the amount of labor to check compression, you might as well just check and set your valves. I check mine every spring.
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Old 05-18-2009, 10:57 AM   #3
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Hard starting and dieing a idle could be a few things, low compression for one, valve to tight-but would run poorly at hi rpm as well, idle circuit too rich. A good tune up cant hurt, do the full meal deal, check compression, check valves, new plugs, adj idle mixture.


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Old 05-18-2009, 11:04 AM   #4
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If your wondering if the valves need adjustment, then they most likly do.
Any clue when they were last adjusted?
After valve adjustment, some carb adjustments may be required as stated above.
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Old 05-18-2009, 01:25 PM   #5
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Valve clearance has a profound influence on idle mixture, the wider the gasp, the richerthe idle circuit behaves, and visa versa.

Sounds like too tight, close to riding, valves to me.
My '84 R100 did this when I was trying to find out if the valve seats were unleaded or not (just in the changeover period), turns out out they were not, and it started to do as you describe on a trip.
Reset the clearances and all was right, now feeding the bike valve saver until I get the heads rebuilt as unleaded.

On old dungers, like air head boxers and Guzzi twins, if you can't hear the gentle symphony of tappets, they are too tight.
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Old 05-18-2009, 01:31 PM   #6
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Sounds like a tight valve and if you are going to do a compression check, you will need to know if the valves are at least adjusted right to eliminate that question from the test. Some bikes like to be a little looser than spec but save that for later and just make sure it's within spec. Good luck.
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