have you tried to pull start it? when we did our kit the decompression arm won't let the engine fire so we removed it alls good now. starter wont turn the engine over fast enough is the reason for the pull start

 

Do continue checking the more simple stuff first, but depending on exactly what happened when the spring in the tensioner went bad it could have created some other things to check.

If the chain was lose enough for it to jump timing it could have caused the valves to hit the piston, and depending on how much it jumped, and what clearences you have the valves could have just lightly rubbed or even hit the piston hard enough to cause them not to seal properly.

I have seen it happen with barely visable damage, and then there are those ones that got ugly, but if all else fails its something else to check out (if the valves are seating properly etc.)

I see compression being brougt up a few times, and unless you somehow checked it wrong you should be fine at 120lbs, and I believe the honda spec is a range and between 115-135 but I can check if you really need to know.

To be honest it just sounds like its one of the simple things and I would really check over the elec stuff again, and be sure its spinning fast enough (charge up that battery!!) and go over the fuel delivery again (maybe remove the air box and tube and look to see if the carb is working and spraying fuel properly etc).

Keep us posted.

 

Sorry for taking so long to update everyone. I did put in a new spark plug, swapped out my rev-box with a known working one (HN1) and still nothing. I will go through the carb again and post what I find. I still haven't attempted a pull-start yet but when the battery is fully charged and cranking fast, the engine backfires extremely loud, but no other popping or starting noises.

 

maybe somethin to look for in your carb is, to see what jets are in it, someone may have put the incorrect jets in it and never did anything about it except for let it sit, becuase when i was meesing with jets, my bike wouldnt run it would just backfire

wreckless

 

I wanna say it had a 170 main in it...? I'll check it out and post later...thanks

 

check your fuses by your battery

 

Which fuse? I'm getting spark so the ignition fuse "should" be fine, but again, I'll check and keep you updated.

 

I swear this is deja-vou (sp) for me when I went through the same mind boggling simptoms and replaced parts that didn't need to be replaced only to find a bad spark plug cap. I had, what I thaught was, a good spark but it was not good enough to run the engine. I found it on accident when I got in the way of the spark and only felt a small, almost unnoticable, zap.
Anyway, you need to do a spark check on it. I bought a spark gauge which is a tool that goes in the plug boot in place of your spark plug. It allows you to open the distance that the spark has to travel so you can measure the quality of the spark. I got mine at Napa but I have seen them at other auto parts stores as well.

 

JS,
You are suggesting then that the plug wire and cap are at fault? Is there a way to check the coil specifically as well? Thank you!!!

 

You can do an ohm test on it but I don't have the value that you would be looking for. Maybe somebody can come up with it, it should be in the service manual.
I'm not sure about the 400EX but most plug caps have a resistor in it that can go bad. Thats what mine did. You really need to do the spark check. If you have an old (known good) plug around you can open the gap up to 3/16" to 1/4" and see if it will fire with your coil. Without the spark test tool thats all I can suggest