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YZ250 to a YZF450

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Hey guys, I am new to the website and figured that I could use a bit of expertise. I am currently in the process of selling my 2-stroke 98 yz250 and replacing it with an 05 yz 450 when the funds roll in and a bike is available. My question has to do with my old bike. At an increasing frequency, my old 2 stroke is fouling plugs. So much so that I carry at least 2 with me on every ride. I don't know the stock jetting and could use some input on possible solutions so that I can sell it with a clean conscience and move on to a more dependable, more efficient 450. Any suggestions are welcome. I ride between 2 and 3 thousand feet with an NGK B8ES plug with a fuel mixture of 40:1. I run an FMF Gold series pipe with an FMF Shorty silencer. The carb is clean and other than the FMF products, the bike is bone stock. I don't ride enough to need a new top end and compression is still good. Please give me specifications as to all jets if possible, idle position, air skrew position, throttle pin placement, and whatever else you might have for me. Also, sorry to bring up 2 strokes as a newcomer. I will be buying a thumper very soon and look forward to it more than you know. Thanks for your input and help.

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dont know if you have a spark arrestor or not, but my old cr250, I could ride all year on the same plug when I had the stock exhaust with a clamp on cobra sparky (that I cleaned on a regular basis). I then switched to a used aftermarket turbine core spark arrestor (which I never cleaned or rebuilt). I went through a ton of plugs before I realized that it was all carboned up and needed new packing. Once I cleaned and repacked, the bike ran like new again.

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sounds like a crakcase seal (oil is leaking in from the gearbox). your complaining about a 6 year old bike... if you think a 450 is going to be more 'dependable' you are in for a big suprise :thumbsup:

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If you get a chance, ride a CRF450 a few times. I know lots of guys that have from the YZf to a CRF. The only reason i have a YZF is because I smokin deal on a tricked out bike that was riddin by a guy who was scarec to death to get of second gear. No kidding!

Keep in mind that the four stroke is going to require a different riding style but once you get the hang of it, it's doubtful you'll ever go back. I hated my CRF the first three rides and was kicking myself, but that's in the past. I'd never ever buy a two smoke again!

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I have never fouled a plug on my KX. My first guess would be that your jetting is off. One thing you can do is get on FMF website or call them and see what they recommend for jetting specs for their exhaust system is and start there. Also you can do the spark plug test to check if your main jetting is on. Ride the bike, get it into 2nd or 3rd, pull the clutch in and hit the kill button and coast to a stop. Pull the plug, Dry& and light tan color=correct, Whitish=lean, wet and sooty black=rich. You can try also tuning the air screw (in-richer, out is leaner) If you the turning scew does not make any difference (you will hear the difference as you are turning it) then you can change out the pilot jet. My bike has a standard plug and a hotter plug. My bike has always run better with the hotter plug. You can try that also. I would assume you are running rich on either the pilot or the main or both. FMF can probably give you a good starting point. It is just going to take some trial and error.

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