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2004 YZ250 Dieing at higher rpms...

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So I recently bought a mint looking 2004 yz250 it runs nice all way around but first rides out I fouled a plug and about 30 after that, we decided to raise the float height to the recommended spec and I stopped fouling plugs. (I have no idea why I said that it was irrelevant) Since I got it if I winded it out past 3/4 it would sometimes die or sputter like crazy them start to idel weird, when it dies only way I can restart it is to pop start her. when it sputters and idels weird and when I turn her off and try to start her again I have to pop it, it won't start by kicking it after these things happen. Anybody know whats up with her? need help fixing it cause going around the track is kinda hard not being able to wind her out! If you have any more questions let me know 

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Start with the simplest thing first. Pull carb and verify jetting. Personally I would completely clean the carb and get a rebuild kit. When I say "clean" I mean soak in yamalube carb soak. Don't just spray carb cleaner and think it's good. Make sure the rebuild kit you get has jets. Once you get the carb right, if it still shows symptoms, we can look elsewhere.

Loosen your rear chain, it's way too tight.

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On 2017-5-17 at 1:21 PM, HunnerBunnerGo said:

but first rides out I fouled a plug and about 30 after that, we decided to raise the float height to the recommended spec and I stopped fouling plugs. (I have no idea why I said that it was irrelevant) Since I got it if I winded it out past 3/4 it would sometimes die or sputter like crazy them start to idel weird, when it dies only way I can restart it is to pop start her. when it sputters and idels weird and when I turn her off and try to start her again I have to pop it, it won't start by kicking it after these things happen.

Everything you wrote suggests it is running too rich. Too much fuel and not enough air.

Assuming the jetting that is in it now once ran fine, then the problem could be:

0. Stale old fuel.
1. the air filter is not flowing air properly or
2. Your piston+rings are badly worn.
3. the previous owner used a different type of fuel, or
4. He used much more premix oil in the fuel than you are, or
5. your exhaust is somehow clogged. or
6. Your reed valve petals are cracked.
7. etc.

You'll have to keep feeding it new spark plugs until you fix it. Stick with 32:1 premix ration for now.

Try a freshly and properly oiled air filter.

Remove the pipe and muffler. Pull the muffler apart and check it's not blocked or clogged.  Put your garden water hose inside the pipe and ensure water flows through it without restriction caused by a dead rat or whatever.

Measure your kick over compression (throttle held wide open) with a $10 compression tester. Should be at least 160 PSI.

If no joy then inspect the reed petals and when the carb is off remove the jets and needle and check the jetting to see how it compares to stock jetting in your owners manual.

After it is fixed and correctly tuned you should never foul a spark plug and never have black oil dripping anywhere from the exhaust system.

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How doe

On 5/16/2017 at 7:21 PM, HunnerBunnerGo said:

So I recently bought a mint looking 2004 yz250 it runs nice all way around but first rides out I fouled a plug and about 30 after that, we decided to raise the float height to the recommended spec and I stopped fouling plugs. (I have no idea why I said that it was irrelevant) Since I got it if I winded it out past 3/4 it would sometimes die or sputter like crazy them start to idel weird, when it dies only way I can restart it is to pop start her. when it sputters and idels weird and when I turn her off and try to start her again I have to pop it, it won't start by kicking it after these things happen. Anybody know whats up with her? need help fixing it cause going around the track is kinda hard not being able to wind her out! If you have any more questions let me know 

Capture.PNG

how does your sparkplug end up looking after you try to wind it out?  

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Well, I think I figured it out... well, there was a small pebble in the venturi stuck in the cut grooves removed it and slapped her back together and decided to rip to the local track and it felt like it had more power and winded right out no problems at all :thumbsup: also kinda surprised I took the pipe off and looked at the piston and rings thing looks brand new! A freaking craigslist bike with a new top end!  oil is still seeping out the exhaust port though a lot? Now the kinda big problem. the second I turn her off since I de-pebbled the carb it just starts pouring gas out the overflow. I'm thinking that is just the float height, thinking i may have bumped it and bent it a little. So! she is basically fixed other than the carb  raining gas when shes not running! so thanks for the help 

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2 hours ago, HunnerBunnerGo said:

A freaking craigslist bike with a new top end!

LOL. No way. You're smokin some good stuff.

Black oily spooge means it's running too rich. Don't seal your pipe or use less oil. Just fix the jetting.  Many threads on it.

I don't understand how something stuck in the carb made it run too rich, but it don't matter. It's fixed. Or semi fixed.  Bit of a worry how some crap got into the carb throat in the first place. Sounds like an air filter problem.

The float valve can be a bit fussy. The rubber tip can be old and gets hardened and they leak out the overflow. Or the can be brand new and tacky and sometimes stick closed.

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