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Last week, I bought a 05 400ex. Seller told me that the engine was completely stock, never opened, and he even had the title for it. Went over the quad with a fine tooth comb and didn't notice anything out of the ordinary. If nothing else, it was completely in tact down to the plastic retainers. There was nothing to indicate that he was being untruthful. He was able to provide a maintenance history on the quad down to the type of oil he used every time he changed it. After seeing nothing but junk from other sellers, I figured this was the best buy considering the maintenance history.

Modifications
Full Yoshimura Exhaust-Said carb was jetted for the exhaust
Bigger Oil Cooler
Aluminum battery/intake box
K/N Air Filter

After getting it home, I noticed the first couple times I rode it that it was a little hard to start but nothing a little choke and a blip of throttle wouldn't fix. Even though it started a little rough it ran strong, idled well, and seemed like a good buy considering I have wanted one of these since I was 15. Anyways, I went through adjusted clutch lever and brake lever to my liking and I gave her an oil change for good measure. Went out to ride with my son around the yard yesterday and coming out of a turn in 2nd/3rd gear the quad lost power and shut down. Spent 15 minutes trying to get it started with no luck so I pulled it into garage to take a better look at it. When I was trying to start it, the motor was turning over but just not firing figuring maybe there was an issue with the carb, I took it apart to clean it and check to see if any jets were clogged since the seller had stored it for the winter before I bought it. Broke the carb down and didn't find anything I noticed to be an issue even the jets were clean (could see through both of them). Put everything back together and tried starting. Now the quad would start but then shut down as soon as I gave it any throttle. After going through this process over and over, it started up and actually idled so I figured I would take it for a spin to see if there was any more issues. Got 1/8 mile down the road to turn around and the quad stalled again. Fiddled around with it and finally got it to start and run long enough to drive it back home, but I noticed an occasional odd sound coming from the ride side of the case. Got it back into the garage and started tearing into it again. This time in the air box, I noticed the negative battery post was loose. While screwing with that, I bumped the positive terminal against the box and blew the 10 fuse. Ran and picked up a new fuse, got back home, put new fuse in and tightened the negative battery connection down but while looking through the wiring I noticed one of the red wires in the battery box going to the (starter solenoid?) was bear so I taped that up to protect it from any shorting issues. While I was this far, I decided I wanted to pull the plug, check for good spark (which there was), and ultimately replace the plug since it is such a PITA to get to anyway. Once I realized the spark was fine and no more loose connections, I decided to take a look at the cam timing just to make sure that there was nothing aloof there because of the odd sound on the right side of the case. In the pictures you will see what I found. With the timing mark on T on the flywheel, cam lobes all facing down, it appears as though the cam timing might be off by a tooth or too? If it did jump a tooth, does that mean there was piston/valve contact i.e., bent valve and/or piston damage as a result? I have literally ridden this thing for no more than an hour since I got it home last week and I am not sure where to go from here. Any advice or suggestions would be very appreciated because the wife was pissed when I bought it to begin with, I can't imagine what she will say if I have to drop several hundred dollars on it to get it back up and running.
 

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