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Power valve failure for too rich?

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I have a 1996 yz 250 two-stroke. I bought this bike over a month ago and thought it had a jetting problem. It would bogged out and I would pin it and it would still bog and then eventually rise up and want to take out from under me. I thought it was running lean so I changed the clip position on the needle down to give it more fuel, it seemed to help out a lot but at certain times it would do the same thing again. The Yamaha shop requested I read jetted the bike one size up of Main and pilot jet from stock. I did and got the same results bogging at low and no matter how much I Clutched it. Occasionally it would run perfect! Than it don't fail.. It Boggs once again. If I put it in neutral and rev it sounds fantastic but when I put it in gear and rev with the clutch in the matter how high I keep the RPMs up soon as I let go it Boggs I can hold wide-open and then eventually it will clear up and rise out from underneath me, again .. occasionally. My dad's friend brought it to my attention that the power valve may be sticky. The last time I looked at the power valve it was pretty confusing and was very very very dirty. May I mention that Unburnt gas is pouring out of the power valve seal constantly. I was told that this probably means the bike is running to Rich or the power valve is sticking closed. But sometimes it rises so I'm thinking it might be sticking occasionally. Can I take off the right side of the power valve and rev the bike in neutral to see if it's lifting thus opening?. I seen a kid do it on a RM 125 but I want to make sure it's safe to have the power valve cover off while the bike is running as long as it's a neutral. Talk me through how to go about this because this is my first 250 two-stroke bike. I'd appreciate any tips or recommendations, thank you all!!

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