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YZ 250 does nothing but foul plugs

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MY 01 yz 250 does nothing but foul plugs when it loads up. If it is blown out properly it will ride all day, but if it has been sitting for any longer than a week it will foul. I have a whole toolbox drawer full of plugs and was wondering if im mixing the fuel too rich (32:1 as suggested in the owners manual) or if i have a jetting problem. Any input would be helpful.

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Brumy, assuming the jetting is close to stock, start by adjusting the pilot air screw(the small screw adjustment - not idle adjustment) on the side of the carb. warm up the motor then, by slowly turning the screw in then out (high idle speed for this) find the adjustment that sounds crisp but not too lean.

Another thing to check is the spark plug cap. They can look fine but be broken internally, causing the spark to have to jump twice. I bought a brand new 76 rm370 back when they 1st came out only to have it foul plugs like a pig. I finally inspected the cap and found the screw that taps into the plug wire broken.

Replaced it and I don't recall ever fouling another plug in 5 or so years of abusing that bike.

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you might also have a blown right side main seal. Do a leak down to check to see if your motor is not sucking tranny oil. Would burn bright white if it was, but a little tranny oil will foul the plug way easier than alot of pre mix.

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Another thing to check: do you turn the fuel valve off when it's parked for days? A leaky float valve in the carb will allow fuel to seep past into the crankcase where it pools up and causes fouled plus as the engine struggles to burn all the excess fuel/oil.

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some ideas to go along with the replies above :

Depending on the oil your using ---If your running full synthetic oil go 50:1, 32:1 would be for your yamalube. I had an 01 that had a tendency to foul the odd plug also. you may want to run a hotter plug for a bit, but I will bet the problem is in the jetting some place. Never clean up a foul plug and reuse it, they may still work, but odds are they wont last, and they wont be good to use when your trying to trouble shoot, toss them.

find a nice long hill to jet on and run it up the hill at different throttle openings, and pay attention how it runs in that spot to help tune the jetting.

If its leaking gas out the tubes just sitting there or at a slight angle you may aslo have a float problem.

before you park it, turn off the gas and clean it out good by reving it out a few times.

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