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2003 400EX wont start


Texan91B
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I bought this quad not running. The previous owner started putting an XR400 engine into it and had started taking apart the 400EX motor. He said the piston was shot on the 400EX. I took it apart the rest of the way and found out the piston was busted and scrathced and so was the bottom of the cylinder. I took the XR400 engine back out and took the whole top end off and put it on the 400EX bottom end. When I put it together I put the piston on TDC with the T showing in the timing window and installed the cam with the two marks even with the head and the 3rd pointing up. Before I put the carb back on I hit the throttle to see if fuel was squirting out and some did. I checked to see if there was spark and I am getting a nice blue spark. The decompression plunger and spring are in still and seemed to be ok when I pushed on it a little. Hit the starter button, engine turns over, piston moves up and down, cam turns. Still wont start. I dont have a compression tester or a feeler gauge so I am trying to rule everything else out before I spend the money for those. Any ideas would be great. I just got this quad and never rebuilt one before. Although I have been an Army mechanic for the last 5 years and do my own mechanic work so I do know most of what I am doing.

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