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Friends '04 having issues, low comp, stuck idle screw, running lean (?)

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So, the bike in question isn't mine. Its My friends. He just got the bike from his dad, and I squeezed as much info out of him as possible. I'm the one with mechanical expirence in our group of friends who ride, so he's come to me for assistance. Heres what I've gotten from him.

'04 KX250F

Low compression (apparently that happened overnight...?)

Idle screw stuck in. Let me elaborate. He turned it in in an attempt to raise the idle (lord knows why...) and it got stuck. Wont turn out, won't turn in.

Exhaust gets bright red. That's why I said it was running lean. Apparently that happened after the idle screw incident...not sure if it just needs a carb clean, or a valve adjustment, or what. I've cleaned 2T carbs, never 4T. The bike has an FMF Megabomb and an FMF Q4.

Also, this happened last year. Some sort of coolant plug popped out. What does it do?

1366245735716.jpg

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So, the bike in question isn't mine. Its My friends. He just got the bike from his dad, and I squeezed as much info out of him as possible. I'm the one with mechanical expirence in our group of friends who ride, so he's come to me for assistance. Heres what I've gotten from him.

'04 KX250F

Low compression (apparently that happened overnight...?)

Idle screw stuck in. Let me elaborate. He turned it in in an attempt to raise the idle (lord knows why...) and it got stuck. Wont turn out, won't turn in.

Exhaust gets bright red. That's why I said it was running lean. Apparently that happened after the idle screw incident...not sure if it just needs a carb clean, or a valve adjustment, or what. I've cleaned 2T carbs, never 4T. The bike has an FMF Megabomb and an FMF Q4.

Also, this happened last year. Some sort of coolant plug popped out. What does it do?

After what you've been through with your 250 Lethal your really stepping in it now, lol. Where to begin? The valves most likely need to be shimed. Pull the carb and clean it, pay attention to the slide if you pull it out. It has a floating plate that can be installed upside down. There is an accelerator pump on the bowl, pull the cover off check the diaphram for cracks, clean and re-assemble. Install a 42 pilot jet at a minimum and have a 45 on hand. Fuel screw set around 2-1/2 turns. On these thumpers there is a fuel screw as opposed to the air screw on your KX so it works just the opposite of yours. Time the accel pump. If your riding woods and lugging alot put in a size 40 leak jet, very small jet in the bowl. The plug was for an optional de-compression lever that was never put on these bikes, thank god. You need to replace it before riding, it is an open hole to the top end of the motor so oil will pour out. As for the idle screw you will have to work at it. And clean the hot start plunger before it gets seized like this one - http://www.thumpertalk.com/topic/1012323-fcr-seized-hotstart-removal/ . The red pipe is normal with no air flow.

Edited by Joshx221
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After what you've been through with your 250 Lethal your really stepping in it now, lol. Where to begin? The valves most likely need to be shimed. Pull the carb and clean it, pay attention to the slide if you pull it out. It has a floating plate that can be installed upside down. There is an accelerator pump on the bowl, pull the cover off check the diaphram for cracks, clean and re-assemble. Install a 42 pilot jet at a minimum and have a 45 on hand. Fuel screw set around 2-1/2 turns. On these thumpers there is a fuel screw as opposed to the air screw on your KX so it works just the opposite of yours. Time the accel pump. If your riding woods and lugging alot put in a size 40 leak jet, very small jet in the bowl. The plug was for an optional de-compression lever that was never put on these bikes, thank god. You need to replace it before riding, it is an open hole to the top end of the motor so oil will pour out. As for the idle screw you will have to work at it. And clean the hot start plunger before it gets seized like this one - http://www.thumpertalk.com/topic/1012323-fcr-seized-hotstart-removal/ . The red pipe is normal with no air flow.

Wow. This is great advice. I've never gotten the chance to hop on and start kicking, although I have pushed it over with my hand and it feels like everyone else's 250F's.

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Wow. This is great advice. I've never gotten the chance to hop on and start kicking, although I have pushed it over with my hand and it feels like everyone else's 250F's.

With the auto decompression on these bikes its pretty normal. I had an 05 kxf before my 03 smoker.

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With the auto decompression on these bikes its pretty normal. I had an 05 kxf before my 03 smoker.

Hopefully its just the carb. Last thing I want to get into it shimming valves. Might turn that one away, lol.

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Ohh the joys of owning the 04-05 KX250f's... Those bikes produced great mechanics / not riders. The only bikes I dont miss having.. EVER... Anyway Josh above is spot on.

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Ohh the joys of owning the 04-05 KX250f's... Those bikes produced great mechanics / not riders. The only bikes I dont miss having.. EVER... Anyway Josh above is spot on.

Oh lord...

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Make sure that the rubber boot where the hot start goes into the carb is on all the way.. Because mine fell off a little and came loose and my rpm's were high and didnt want to run without the choke on. Just an idea about the idle

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