just bought a dead 400 ex , the top end of the bike was removed

so i rebuild the top end , and no start

it has gas ( as i when i remove the plug and crank , you can see the cloud of gas

there is spark, but not sure if it is ok, it seems weak and sparking more often than it should, my timing gun wont pick up the spark signal,

it is timed properly and has lots of compression

i think my CDI is dead , but since you cant return them !!!! , how compatible are they year to year ,, how can you test it , would it be the coil,, have you ever seen a coil go like that

i connected the bike to a car battery to try to start faster but still no luck

any idea, i am running out of leads and hair( pulling them off)

thanks in advance

yves

 

weak spark, good compression, fuel, and the timing light won't pick up the signal?...sounds to me like the timing is 180 degrees off...try adjusting that and see if it helps!

 

i did not have the book , but i have fix all kind of engine for years

so the flywheel/ magnto is at the T mark , wich put the piston at TDC on the firing stroke

so the valve should be all closed, all the lobes down, the 2 horizontal mark match the case and the vertical line pointing up ,, if pointing down you would be at the end of exhaust/ beggining of intake

apparently ,the top end was taken apart because of slap, but i am not sure , i just assume and rebuilt it

 

I am having the same problem. I have done the 180 switch and nothing. now it will pop out exhaust and then in take. so i go 180 again and it does nothing but crank. now with mine I cant get the cam gear just right. i seems like a half tooth off. ive gone a tooth both ways and no luck. any ideas? did you get yours running? plus mine was running before and i just bored it and put a prowell piston in it. 415 kit.

 

Sounds like there's a 400ex virus going around.

 

I had the same problem when I rebuilt an 01 model. I tore down the carb and cleaned the jets, put the carb back together and fired it up. It's been hitting the trails ever since.

 

i tried cleaning the carb and got no where ,, started tracking electrical issue , weak spark, so surfed to find the service manual ( found it ) but computer got nasty virus looking for an other one , the only thing is that i rwad a bit first and i should have 100V from the blacké red wire that is out of the stator wiring and the same color on the CDI ,, i got 35V ,, obviously my stator is dead ,, but i found a guy here that has new one for 150$ RMSTATOR,, they also had CDI for 50$ and they offer the see if it is good service for 25$ , so i will try that