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blown head gasket or bad jetting?

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so, i did a top end on my 2010 kx250f about 40 hours ago and i cant figure out whats going on here. 

ill start the bike when cold, have the choke on, and it will idle correctly but it will then idle down as if i turned

the choke off even when i havent. it will usually idle down within 2 minutes or so. once warm, i can only make it idle either way too high like 3,200rpm or way too low like 1,500. i like to be around 2k at idle but this thing wont go anywhere inbetween. its either super high, or super low. anybody got any pointers? i dont believe its the head gasket but i dont see why it would all of the sudden act like this?

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so, i did a top end on my 2010 kx250f about 40 hours ago and i cant figure out whats going on here.

ill start the bike when cold, have the choke on, and it will idle correctly but it will then idle down as if i turned

the choke off even when i havent. it will usually idle down within 2 minutes or so. once warm, i can only make it idle either way too high like 3,200rpm or way too low like 1,500. i like to be around 2k at idle but this thing wont go anywhere inbetween. its either super high, or super low. anybody got any pointers? i dont believe its the head gasket but i dont see why it would all of the sudden act like this?

look for an air leak

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Is the pipe getting red hot? If so it's lean. If it idles high that's Also a symptom of it being lean. To fix this clean the carb really good. Take the main jet out and run wire through it. Like flossing teeth. If that doesn't work adjust the throttle needle clip. Put the clip down one notch at a time. This will pull the needle up. In turn letting more fuel in. And make sure the f/a screw is properly set. If that doesn't work rebuild the carb with brand new stock jets. One of those should fix it. It not jet the carb. But dot go all out. One size up would definitely do it.

 

 

yesterday i took the carb into work. yanked it all apart and threw it into the ultrasonic tank for a half hour, then the hot tank for a half hour and put it all together. i got home and inspected the pipe for cracks and the air boot. didnt find any so i put the carb on. it seems to run better but i did notice the pipe was glowing pretty quickly. it was dusk outside so that could be part of it. anyways i would give it a rev and it would rev down to say 4k, then a couple seconds later it would come down to idle. 

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Did this problem or curve right after you put the top in on I know with big block Chevrolet if the timing is retarded the exhaust will glow red hot so if your cam timing is off it might be holding your exhaust valves open a little longer and turning your exhaust red if that's an issue not sure the timing of the problem, I do know if the bike was running fine there is no reason to change needles settings hi and low speed jets there's something else going on there's no reason for the carburetor to be tuned differently if it worked fine before

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Did this problem or curve right after you put the top in on I know with big block Chevrolet if the timing is retarded the exhaust will glow red hot so if your cam timing is off it might be holding your exhaust valves open a little longer and turning your exhaust red if that's an issue not sure the timing of the problem, I do know if the bike was running fine there is no reason to change needles settings hi and low speed jets there's something else going on there's no reason for the carburetor to be tuned differently if it worked fine before

it's a 250f the exhausts glow red often.

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