400ex backfiring

[codyslombo]

Hi i have a 2000 honda 400ex and at a idle it idles rough, and then back fires and dies. I have cleaned the carb, it has a k&n air filter and a trx 450r stock muffler. Can anyone help me out.
Thanks Cody

[Ridiculous]

how did you go about cleaning the carb? and is it adjusted proberly? is your air filter clean? is your spark plug new?

just a few questions to get the troubleshooting ball rolling...

[Ridiculous]

glad i could help :rolleyes:

[codyslombo]

Hi i have a new plug for it but i cant get the old one out, is there a speciel socket or way to take it out. and it backfires through the intake/carb not exhaust if that helps

[CJM]

Turn your air/fuel screw all the way in then 2.25 turns out.

You need an 18mm thinwall socket you grind down a bit or the 400ex sparkplug tool

[duneslider]

Probably running lean, did you rejet after the k&n and exhaust changes?

[codyslombo]

It was already jetted for the k&n filter and exhuast and yes i ajusted it to hondas specs cuz i read the hole prosses when i rebuild the carb in the repair manual. so i prob could just grid down a 18 mm socket and that will work?

[CJM]

Yes, but the 400ex tool is MUCH easier to use. Trust me on that one.

You didnt change the jets back to stock, right? Like I said turn the air/fuel screw out to 2.25 or so turns.

[codyslombo]

No the jets r not stock and its ajusted to 2.25 turns out

[codyslombo]

I just changed the plug and it runs alittle better but still pops through the carb and dies. idk wht to do next

[CJM]

Adjust the valves and verify the timing chain tensioner is functioning properly.

Also make sure your intake boot doesnt have any cracks in it.

[codyslombo]

I have adjusted the Valve to where they r suppose to be. The chains good. And it has a brand new boot on the intake. But the decompression is jamed and doesn't let go, so it's not functioning and ticks all the time. But I wouldn't think that would do anything as how it runs at a idle

[CJM]

If its jammed one valve is constantly slightly stuck open.

[codyslombo]

Well not always cuz then it wouldn't run at all and it runs fine at high rome or alittle above idle. And it's jamed like it's not leaving the vlave open it's jamed like it has full compression and not sticking it open at all

[CJM]

I still think thats part of your problem.

[codyslombo]

Yeah and I would really love to fix it cuz it's annoying as hell. But how do you unjam it do you have any idea?

[CJM]

Take it apart? Never seen one jam honestly.

[codyslombo]

the only way i can see you taking it apart is you have to press the flange off the cam where the cam chain sprocket bolts to