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Hey guys, first time poster here. So yesterday I was riding my 2004 400ex, and my throttle stuck about halfway open on the trails. Unfortunate, I know. I hit a small tree, probably around an inch and a half thick. The tree stood no chance and was snapped off, but it was enough to make the quad stop very suddenly. No physical damage was taken to the quad, but now I have a knock every so often from my bottom end. The engine also really does not want to run. Seems to almost misfire when the knock hits. There were no metal shavings in the oil filter either. I would think the knock would be constant if the issue was a bearing blown or something, but I've only owned this quad for a couple of months so I have no idea. Any advice on what this issue could be would be very appreciated. Thank you for taking your time to read this.
 

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When the engine stops suddenly while running at an elevated RPM, it's possible to shear the flywheel key and throw the timing off. The knock you are hearing might be spark knock caused by incorrect timing. I would have a mechanic inspect the timing mark on the flywheel in relation to the position of the piston - this can be done simply by removing the spark plug and setting the piston at TDC then inspecting the T mark on the flywheel to see if the flywheel is in the correct position when the piston is at TDC.

If it other than that, the mechanic can offer suggestions based on the noise that is being emitted.
 
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