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View Full Version : Emergency After Rebuild


wyattearp29
03-18-2009, 08:29 PM
I JUST REBUILT MY 400EX. I PUT A JE 416 11 TO 1 PISTON. I HAVE BEEN BREAKING IT IN OVER THE LAST FEW DAYS AND IT IT HAS DIED ON ME TWICE WHEN I GET UP TO 3/4 THROTTLE. IT HAS BEEN ABLE TO START EVERY TIME BUT THIS LAST TIME IT DIED IT WON'T START NOW . I HAVE GOT FUEL AND SPARK. I ALSO PULLED OFF THE VALVE COVER AND MY TIMING IS ON. SO IF ANY ONE HAS ANY IDEAS LET ME KNOW.
Sanddraging28
03-18-2009, 08:51 PM
did you torque your head down the right way????

did your head studs get put back in correctly???

these are the first to things i would check. i had a problem the the first time i built a 416 years ago....turned out i didnt check to see if the machine shop had put the head studs back in right......they were only finger tight and were pulling out of the head.
honda400ex2003
03-18-2009, 10:45 PM
you could also check the plug and compression while you are at it. good luck, steve
hypersnyper6947
03-18-2009, 10:53 PM
check to make sure your vent is working on your gas cap (yes im serious)

Take you carb apart and clean it, Then put a bigger main in there b/c you prob need it anyways. You may want to put a bigger pilot in there to depending on how your low end was.

During your rebuild did you drain your fuel tank or did the old fuel sit in there for awhile? Also may want to check you petcock valve.
wyattearp29
03-18-2009, 11:40 PM
I will check all the fuel in the morning. I Think my jetting is correct . I did just put a 450r carb on. I have 48 pilot and a 185 main. These are real comparable to some other peoples at my elevation which is 4500-5000 ft. I would really like it to be a fuel problem. I do need to run a compression test but I am not sure if my rings are broke in yet to give me a good reading.
wyattearp29
03-19-2009, 07:41 AM
bad news I pulled the head off and the piston has been rubbing on the cylinder wall.
brian76708
03-19-2009, 08:24 AM
did u put the piston in right the arrow should be pointed twards the front.
hypersnyper6947
03-19-2009, 09:12 AM
who put your wrist clip and rings in, and do you know if it was done right?
jcs003
03-19-2009, 09:15 AM
check all wiring connections and grounds
sc400ex_rider
03-19-2009, 11:54 AM
did you wash your cylinder out with soap and water to get all the metal filings out? that will eat up a piston quick.
wyattearp29
03-19-2009, 09:05 PM
Just an update. It looks light it might have been bored wrong. The rings were pushed in on one side. I took it to a guy and it looks like he might be able to save it but he has to mic it. I also have to.buy a new piston. I did wash the cylinder and I did put the arrow the right way. Thanks for all you input.