why am i having a spark issue under compression?

[richnakol]

I have a 440 ex, 12.5:1 compression, stage 2 web cam port/polish all the bells and whistles. Im having starting issues and running issues. Been at the shop for 2 weeks. They said they ordered a new cdi for it. When the plug is out of the cylinder, it sparks. When it is in the cylinder under compression, it only sparks every other time. Why? whats the fix? is it the cdi? im 600 $ into this in labor for trouble shooting, please help me!

[imc188222]

Does it have reverse? Is it possible that something is up with the reverse switch or wiring and it thinks it is in reverse? I worked on a 250x once that the reverse switch was stuck on and would not start even though there was spark, fuel, compression. Just a thought, not sure if the 400ex uses the same method of keeping it from starting in reverse. I'm sure someone will chime in here.

[richnakol]

its a 2000 and it does not have reverse. Thank you for the response. I hope someone will chime in soon, its the only thing left is help from the forum

[ae13291]

could be a gapping/ or messed up coil that will still give spark but not powerful enough .

[fishnfergie]

When you check for spark out of the jug are you taking the plug out and checking that too or just checking it from the boot?

[richnakol]

to be honest, im not sure. it is at a dealer. This is the info they relayed to me. i know they said it is firing everyother time in the jug with the timing light i believe. when its out? im not sure. the guy who is working on it has a real good reputation, has been to about every honda and yamaha school they offer. Probally has 25+ years between honda yamaha and harley davidson. I would think he would try to change the plug. he said the stator and rectifier all tested good. said the only thing left is the cdi. im not convinced though. was hoping someone else has had a spark problem when under high compression. it runs pretty damn good at higher speeds/rpms. cuts out at low rpms like it is missing. real jerky. that is assuming you can get it to start.

[brokenmike]

I just had a similar problem on my 400ex. It got harder to start to the point it would not even start any more. It had great spark, compression,fuel,and was getting air. It would not even start on either... I couldnt figure it out. I swapped out the CDI,spark plug,and coil with no luck. I had a spare stator so I threw it in there and it fired rite up....

[richnakol]

thank you for the reply. every little bit of info helps!

[richnakol]

just wanted to let everyone know that the issue was the CDI. my bill only ended up being 320$ including the cdi. I was happy. i have had a long standing with the dealership and they took care of me. thank you to everyone here as well