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what is the normal idle temp of a yz250 2-stroke?

This is a discussion on what is the normal idle temp of a yz250 2-stroke? within the YZ forums, part of the Yamaha category; I just rebuilt the top end of my yz250 2001. I was wondering if it is running too hot. So ...


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Old 12-27-2008   #1
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Default what is the normal idle temp of a yz250 2-stroke?

I just rebuilt the top end of my yz250 2001. I was wondering if it is running too hot. So i ran it idle for about 10 minutes, then i took off the radiator cap and used a thermometer and put it in the antifreeze to see the Temperature it read 170 degrees Farenheit. Also when i turned off the bike i could hold my hand to the top head for about 3 or 4 seconds, then i would have to pull away because of the heat.The first time, the piston melted and ruined the top jug. Then I rebuilt it again and then the piston melted again but i only needed to replace the piston and rings. i don't want to do it a third time, so i want to know if it is because by bike is running too hot.can someone tell me how hot it should be after 10 minutes or so of idling?
Josh W is offline   Reply With Quote
Old 01-22-2009   #2
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More than likely its running lean. Learn how to read your spark plug and rejet accordingly. Does it pop and crack when you are riding? That is an indication of lean. Also a new plug will shortly look blistered if it is lean. Do a search about tuning your carb.
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Old 02-16-2009   #3
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Excessive engine temperature doesn't melt pistons and on a 2 stroke will usually seize the engine until it cools down. Melted pistons come from detonation or pre-ignition.Detonation (pinging) is caused by excessively lean fuel-air mixtures or overly advanced ignition timing. The"ping"is actually a shock wave that knocks the protective layer of gas bubbles off of the piston. With these gone, you then have 1200 degree combustion temps directly against aluminum that melts at 800-900 degrees which is where the hole comes from.Pre-ignition is caused by overly advanced ignition or carbon deposits on the piston, head or spark plug. These deposits become red hot and ignite the fuel prior to the spark plug firing. Spark plugs that are way too hot (heat range) may cause pre-ignition as well.Since you've overhauled the engine already, forget the carbon and richen up the fuel mix. Keep in mind that if you have to pre-mix the fuel and oil, too much oil will cause lean running as well because the oil replaces gas in the mix. ------
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