Weird idling problem...running out of ideas

[44oEX]

Hey

I`m fixing up a 400ex for a friend. It just won`t idle at all. At first I figured the idle was just set to low, but now we have the adjustment all the way and still no go. So there is obviously something wrong.

The lack of idle also makes it really hard to start. And onces it does, if you give it some gas, smokes black quite a bit. But the jetting is spot on, if not even a little on the lean side.

Carb is clean, spark plug is new. I was guessing weak spark so we swaped the coil, CDI, and even carb from another EX with no luck.

Valves are set properly. The only thing is that I noticed a little bit if carbon in the intake, so one of the valve is leaking. But I really can`t see that making it not idle. (I know it should still be fixed)

Any more ideas as to what the heck the problem could be?

[CJM]

Could be an air leak. Make sure the boots on the carb are 100% secure.

[MidnightBlade]

mine did the same thing and i realized the choke was on

[44oEX]

Yeah the chokes not on, we`ve been changing parts from other EX`s and everything.

The boots are on there properly, but it might be ripped, i`ll have to check on that.

[killer454]

carbon in the intake tells me you got a intake valve not closing all the way.maybe a bent intake valve when the plug fires fuel/air is burning in the intake if the valve is not closing all the way this would cause a rich condition to.
the intake should look spotless,very clean,check your timeing marks to.

[killer454]

you answered your own question fix the valve,i did not see the last part of your post till now the valve is the problem.

[skip426]

I had what sounds like the same problem with my stock 400. It turned out to be the Stator. It wasn't creating enough juice for the coil to get what it needed. Chased the problem for weeks. If you have a good manual it will have test you can run on the stator and pick up to see if there in spec.
Definatly need to fix the valve though, nothing wants to idle or run right with low compression. ---- Skip

Hope this helps.

[44oEX]

I opened up the motor, ends up the head gasket was blown in 6 places....just no enough compression to keep it idling.