250r cdi on a 400ex

[bhatch21]

Will a stock 88-89 250r cdi work on an early 2000s model 400ex?

[JOHNDOE83]

I think so, the timing may be a lil off, just have to try it and see.

Ive used scooter cdi's before, Ive used coils from street bikes on atv's, anythings worth a try, I heard the 250r cdi removes the rev limiter?

[bhatch21]

Thanks for the reply. I'm curious because I have 2 250r cdi boxes that I am unable to test on anything but a 400ex.

I determined that the 400's wiring harness only has 3 wires going to the 4pin connector. It's missing the ground from the pulse generator. Would this keep the 250r box from firing on that bike?

[bhatch21]

So there's no Honda Man on this site that has both a 400ex and and 250r that could swap the cdi boxes and tell me if the 250r cdi fires the 400ex? Where's the loyalty. I've got 3 banshees.

[JOHNDOE83]

Steve has both, but if you have the 400ex and two 250r cdi's?

Why dont you try it?

[bhatch21]

Oops, I forgot to update this thread. I tried both of my newer 250r cdi boxes on my buddies 400ex and got no spark. I don't know if this is because the boxes are bad, or the 400ex is missing the pulse generator's ground wire.

[honda400ex2003]

it wouldnt work for sure. they the xr250 dirt bike will work though. that is the one that alot of the aftermarket setups use.

the r one has a different spark impulse so it hits at a different time and at a different rate than the ex one or the xr one.

steve

[bhatch21]

Are you sure? The 400ex cdi fires and runs my 250r. And this guy seems to have encountered the famed cold start problem when doing the "box swap": http://forums.atvconnection.com/honda/31172-caution-about-cdi-cold-starting-400ex.html

I think the cdi just sends spark to the plug when it gets a signal from the pulse generator. And that would happen everytime the flywheel tab goes by it, regardless of what motor it's on.

[honda400ex2003]

I havent heard a whole lot honda using the 400 honda. Someone else ran a 400 one and didnt sound like charter had good luck. I didnt say the ex one worked well. It is/charter been known to cause issues when the battery isnt completely charged.

Steve

[honda400ex2003]

theres also a sixth wire on the r one that is an extra ground. without that ground, the cdi doesnt work correctly on the ex. the ex one works since it does not require that ground to operate.

the 400 one acts as though the ground isnt there so it is ok but might sometimes send the signal differently.

i forgot about that until just a second ago so i had to get out of bed and use my laptop instead of my tablet. it was taking too long to type it on there.

steve

[honda400ex2003]

the big gun and the white brothers cdis are also just the xr250 cdi in disguise, thus the cold starting issues that some people have. some will never experience it, while others never get away from it.

my suggestion, keep the stock stuff on there for a reason. theres no reason to run an aftermarket cdi on one of these anyway. get a sparks timing key instead of buying the cdi that advances timing.

steve

[JOHNDOE83]

Originally posted by honda400ex2003
the big gun and the white brothers cdis are also just the xr250 cdi in disguise, thus the cold starting issues that some people have. some will never experience it, while others never get away from it.

my suggestion, keep the stock stuff on there for a reason. theres no reason to run an aftermarket cdi on one of these anyway. get a sparks timing key instead of buying the cdi that advances timing.

steve

I agree.

Ive tryd many different cdi's and the white bros was best, it is just a xr in disguise though.

A timing key even though I havent tryd one, is a better solution.

There was a thread were the guy had a CDI and a key, he couldnt get it to run right, I told him try the stock cdi and it worked and ran fine after that. "to much timing advance"

[honda400ex2003]

lol sorry about all of the posts. my tablet was a pain to try to type on without my keyboard.

i should have edited them but thats ok, it is still readable.

steve

[honda400ex2003]

no i havent personally. I run parts that are supposed to be for the machine its made for most of the time. esp when it comes to motor and electrical.

the r one will not work on the 400ex and if you do not have an r to test a 400ex one, it will be tough to test it.

maybe check the manual and see if there is a test procedure to check the cdi itself.

steve