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2008 TE450-- Bike (still) runs poorly after a half hour

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Hello again,

I made a post about a month ago about my 2008 te450 that would run really poorly after 15 minutes. The guys suggested unplugging my temp sensor and that seemed to solve the problem. I rode it for a few weeks like that, got a new temp sensor installed, and all was well. I took it on some longer rides with a lot of hillclimbs and it ran like a champ. Until yesterday.

I took it down to a local motocross track and started having the exact same problem. After a half hour, I start to hear backfires under even throttle, and over the next five minutes, the bike runs worse and worse until it doesn't run at all. Unplugging the temp sensor at this state doesn't help. I stop and let it cool down and it'll run fine enough to let me limp it home. Its almost like it's overheating, but there's plenty of coolant and the radiator fan never even kicks on (unless I disconnect the temp sensor of course) which is telling me it isn't even running all that hot.

The valves are in spec. The oil and air filter are fine. The radiator cap is nice and hot, so the water pump is working. There's no way the temp sensor failed after two weeks. What the hell is wrong with my bike?

Unfortunately, I seem to be about 1500 km from a decent mechanic so you guys are really my only hope here.

 

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Last mine did this it was found to have bad gas in the tank. Try to change that and add some FI cleaner in your tank.

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New development- i cleaned the engine off because it seemed that it was getting dirtier and dirtier. I suspected an oil leak of some kind, and my suspicions were confirmed. After a 30 minute ride, there was fresh oil on the engine case. Theres some on top of the head, and it seems to be coming from one of the head bolts but i cant be sure. Was the head not torqued on properly? (i had the valves checked recently) What does it mean if my bike leaks oil from the top end when it gets hot? does it need a head gasket or what? My guess is, this is the source of my problems-- loss of compression when it gets hot, and under high revs

20170521_174132.jpg

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Is the oil coming from the valve cover gasket? If so, then that's not the cause of your problems. I've heard of coils doing that after they get hot. Not sure if there's a way to test it other than swapping a known good one for it. Good luck. 

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Just thought of this, take a ride and get her hot, bring tools to pull the plug. If/when it dies, pull the plug, put it back in the boot and check for spark. My $'s on an electrical problem.

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Oh yeah, since you had your valves checked maybe they didn't tighten up the valve cover bolts good. Check them to see but don't go crazy, they're low torque bolts. Also could be coming from the plastic fitting that hose connects to. They've been known to crack and leak. Some RTV could cure that.

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