Hi, i have a 2001 400ex recently rebuilt the motor new piston,rings,jug, timing chain, tensioner, timing chain guide. got it back together everything seemed to run fine adjusted the valves while it was apart, wouldnt idle just figured it need jetted. I was driving it today going about half throttle then all of the sudden started ticking and shut off loaded it on the truck and took it to the shop, one of the valves tightened up, reset the valves put it back together worked better and would idle once i got it warmed up. brought it back and it was smoking it was running way to hot the felt/foam on those black side fenders stuck to the frame. Was wondering if anyone could tell me why it would be running way to hot. last time i had the motor apart the only way it would start is if we advanced the timing one tooth, so did the same this rebuild and started right up fine, put a new fmf powercore 4 with powerbomb header on last summer had a k & n air filter motor is stock, didnt rejet when i put the exhaust on seemed to work just fine without rejetting. where i live is about 200 ft above sea level temp is anywheres from -30 to +10 Celsius right now. the header pipe starts turning cherry red almost instantly. bought a dynojet jet kit just came with the main jet's. going to try timing it again tomorrow, so any help would be greatly appreciated.

 

You are running super lean. Any time you mod the exhaust, filter or motor you need to rejet.

 

just wondering why all of the sudden it would be running so hot? also have you ever heard of having to advance the timing on the 400's to get them to start? and thanks for the reply.

 

Got it fired up, my old timing chain was stretched thats why i had to advance the timing and when i put the new chain on it wasnt in time. my jet kit only came with the main jets and the needle didnt come with a pilot jet, so been trying to get the jetting figured out getting close, have a 38 pilot and 146 main it will sit there and idle perfect, can rev it up sitting there it dosn't bog or back fire, but when you go to drive it then it spits and sputters im assuming its getting to my gas, so going to try a 142 main jet and see if that cures it.

 

Did you go with a bigger piston? I think you want to go up on the main jet. If it runs good until about 1/4-1/3 throttle then bogs after that means you need to get a bigger main. Try a 155.
What timing advance key do you have, +3 deg or +6 deg? Advancing the timing will make it run a little hotter. The +6 deg key is not recommended with a high compression piston.

 

went with a 155 main started/idle/worked good like it should drove it for 20 mins up and down the road then parked it then few hours later took it out drove it about 2 kms worked really good then i noticed in 5th gear it just seemed to lose its power brought it back and it stalled in the drive way checked valves everything seems good only thing we could figure out its not getting enough gas, we sprayed gas in where the spark plug goes and it would start then and run, checked the plug, plug is bone dry and its brown. also i dont have a timing advance key it was just the timing chain stretched and for some reason only way it would start was with the cam advanced one tooth then when i bought a new timing chain it had to be in time without advancing it to run good. running out of ideas theres fire only thing i can think of is maybe a peice of dirt in the carb.

 

When your plug is brown that means your jetting is good. What do you have the fuel air screw adjusted to? Like you said try cleaning the carb.

 

took the motor apart need new piston and rings, when it got hot it melted the rings to the piston. only had about 30 km on that motor job lol. live and learn i guess, thanks for the help.